OKLCH is a polar coordinate space. Hue is angle in this space. So to interpolate hue from one angle to another, to get from one side of a circle to the other, you go round the edge. This leads to extreme examples like the one shown:
linear-gradient(in oklch, #f0f, #0f0)
You can also go round the circle the other way, which will take you via blue–aqua instead of via red–yellow:
linear-gradient(in oklch longer hue, #f0f, #0f0)
The gradient shown (in either case) is a good example of a way that perceptual colour spaces are really bad to work in: practically the entire way round the edge of the circle, it’s outside sRGB, in fact way outside of the colours humans can perceive. Perceptual colour spaces are really bad at handling the edges of gamuts, where slightly perturbing the values take you out of gamut.
Accordingly, there are algorithms defined (yes, plural: not every application has agreed on the technique to use) to drag the colour back in-gamut, but it sacrifices the perceptual uniformity. The red in that gradient is way darker than the rest of it.
When you’re looking for better gradients, if you’re caring about perceptual uniformity (which frequently you shouldn’t, perceptual colour spaces are being massively overapplied), you should probably default to interpolating in Oklab instead, which takes a straight line from one side of the circle to the other—yes, through grey, if necessary.
linear-gradient(in oklab, #f0f, #0f0)
And in this case, that gets you about as decent a magenta-to-lime gradient as you can hope for, not going via red and yellow, and not exhibiting the inappropriate darkening of sRGB interpolation (… though if I were hand-tuning such a gradient, I’d actually go a bit darker than Oklab does).
During its beta period, Tailwind v4 tried shifting from sRGB to Oklch for gradient interpolation; by release, they’d decided Oklab was a safer default.
nkrisc · 12m ago
IMO in pretty much all cases if the two colors at the end of your gradient are not already very close, you will always get the best results by manually specifying the colors at one or more steps between the two original colors.
Which brings me to point at the crux of the matter: avoid gradients between two dissimilar colors in the first place.
Diggsey · 5h ago
Also, isn't the way browsers interpolate colors in sRGB just a bug that I assume is retained for backwards compatibility? sRGB is a logarithmic encoding, you were never supposed to interpolate between colors directly in that encoding - the spec says you're suppose to convert to linear RGB first and do the interpolation there...
spoiler · 1h ago
It's not a bug, its a property of the colour space. Which is partially tied to how the colour is represented (RGB). When doing linear interpolation through the RGB cube (for eg a gradient), you normally pick the shortest path. It just so happens that sometimes that path passes thorough some shade of gray as different colour components are scaled.
Usually you fix it by moving your point through a different colour space. Choice depends on your requirements and mediums you're working with (normally different types of light sources or screens).
I had to write a low level colour interpolation librar for a few interactive art projects, so I dipped a bit into this, but I'm no colour expert
Diggsey · 11m ago
No, sRGB refers to both a colour space and an encoding of that colour space. The encoding is non-linear to make best use of the 256 levels available per channel, but you were never supposed to interpolate sRGB by linearly interpolating the encoded components: you're supposed to apply the transfer function, perform the linear interpolation at higher precision, and then convert back down into the non-linear encoding.
Failure to do this conversion is what leads to the bad results when interpolating: going from red to green will still go through grey but it should go through a much lighter grey compared to what happens if you get the interpolation wrong.
Sharlin · 37m ago
I think GP is referring to the difference between "normal" (gamma-encoded) sRGB and linear sRGB. Though it's not logarithmic but a power law. In any case linear interpolation done in non-linear sRGB gives you intermediate colors that are darker than they should (though historically it's been so common in computer graphics that people are accustomed to it).
jakubkrehel · 3h ago
This is super insightful, thank you! I wrote the article and will make changes to explain this better :)
For others, I'm sure parent knows: OKLCH is largely a bugfix for CILEAB. Both try to make a color space where even steps feel evenly spaced to a human. But CIELAB had procedural flaws in its creation.
See slide 19: https://www.w3.org/Graphics/Color/Workshop/slides/talk/lille... -- if you ask CIELAB to make "pure blue" (RGB 0 0 100%) become grayscale, the intermediate colors become purple to the human eye. The entire point of a perceptual color space is that that doesn't happen. OKLCH fixes that.
BTW, credit to Björn Ottosson, who basically side-projected a color space into the web standards and more: https://bottosson.github.io/posts/oklab/ ... folks like him are why we sometimes have nice things!
djoldman · 4h ago
But what really is a "color gradient"?
Isn't it any continuous function that starts at a specified color and ends at another specified color?
How then does one say that any gradient is good or bad?
Isn't the problem you are highlighting guaranteed to exist for any colorspace that defines colors outside of human perception?
layer8 · 4h ago
A good gradient is one that takes a perceptually uniform, and typically perceptually shortest, path. The OKLCH gradient isn't perceptual uniform and appears to take unnecessary detours through other hues.
cubefox · 3h ago
One could also argue that the detour through other hues is necessary in this case to avoid going through grey.
layer8 · 3h ago
Gray is arguably just another color, it’s not clear why you’d want to avoid it. How is going via red and yellow better than going via gray? Varying hue is often perceived as a larger change than varying saturation or lightness. A path going through several distinct hues is visually less uniform than one going through gray once.
brulard · 1h ago
Let's say you continuously change wavelength of a laser from blue (~480nm) to red (~630nm), you are going through green, not through gray. If in your use case going through gray makes sense, that's ok, there may be many paths from one color to another.
Sharlin · 27m ago
In general people don't really think of color in terms of the spectral progression (or the hue wheel), and I don't think that most people intuitively expect a gradient between two colors to pass through another "unrelated" primary or secondary color. The point is somewhat moot though, given that such gradients (like yellow to blue or red to green) are very unnatural anyway.
the_af · 2h ago
Is gray perceived as "just another color" or where all colors go when desaturated? I assumed the latter, which would explain why to avoid it if one isn't playing with saturation.
layer8 · 2h ago
Think of fashion, of smartphone colors, pen and pencil colors and the like. Gray, white, black, are just color choices among all the available colors. A gray T-shirt isn’t a desaturated colored T-shirt. It’s its own color.
the_af · 1h ago
Oh, I understand what you say. But in color spaces, isn't gray the "sink" towards which desaturated colors shift? This would make it a location to avoid (unless you're purposefully desaturating).
cruffle_duffle · 59m ago
Color is weird like. Gray is “all the visible spectrum in equal proportions”, which is white… just less white than the whitest thing visible but more white than the darkest (blackest) thing visible.
It’s a “color” because it’s useful to describe such a thing. If you had monitor entirely filled with 50% white you’d call it white. Only by comparing it to something brighter do you call it gray. Brown is the same thing. In a dark room if you looked at a monitor filled with red and green pixels you’d call it orange. Only when you start adding in clues like whites and brighter colors would you call it brown.
Anyway, yes grey is a color. But it is not quite the same as other colors. Other colors occupy only parts of the visible electromagnetic spectrum. Whites are the whole thing.
There is actually several very good technology connections videos about this stuff. Color is very cool!
AnimalMuppet · 45m ago
It depends on how you think about your spread. If, as someone else said, you're trying to represent a tunable laser going from red to blue, going through gray is completely wrong. That is not what a laser will do, ever. It will always be a fully saturated color.
So, depending on what you're doing, you want different things. You may want to view your color space as an RGB cube, and go through gray. Or you may want to view your color space as something more like HLS or OKLCH, and not go through gray.
Vingdoloras · 8h ago
For anyone else copy pasting the gradients into dev tools to look at them: The second one is missing the # sign on the first color.
And yes, both oklch gradients look pretty weird while the oklab gradient looks nice (if you can accept it going through grey).
hammock · 3h ago
Can anyone share some images for those who don’t have dev tools to view them?
chrismorgan · 8h ago
Sorry, fixed.
ta8645 · 9h ago
Very interesting. Is this just a limitation of our current hardware? How much of this problem would still exist if everyone had a wider gamut monitor, say full DCI-P3? That still doesn't cover the full gamut of Oklch, but would it make the problem practically disappear?
chrismorgan · 9h ago
No. We’re talking about colours way beyond the ranges of human perception.
For this specific gradient, see https://oklch.com/#0.7017,0.3225,328.36,100 and https://oklch.com/#0.86644,0.294827,142.4953,100, and look at the Chroma panel, see how far out of our screen gamuts they are (even tick “Show Rec2020”, which adds a lot of chroma around blue–green and magenta–red), and try to imagine the colours between the lime and magenta (in either direction). The red direction is probably the easier to reason about: there’s just no such colour as a light, bright red. You can have bright or light, but not both. (Its 3D view can also be useful to visualise these things: you’re building a straight-line bridge between two peaks, and there’s a chasm in between.)
shrx · 8h ago
I don't get it, why am I seeing the "out of gamut" colors if my sRGB monitor is unable to display them? Would the charts look different on a P3 monitor?
edit: Also, you mentioned the colors "beyond the ranges of human perception" but I don't think there is any such limitation here, the bottleneck is the hardware (computer monitors).
chrismorgan · 8h ago
It’s squashing the range of the colours down to simulate it.
the_af · 2h ago
I don't understand why HN sometimes responds aggressively to an honest, puzzled question. It's as if being wrong (or confused) was a sin here, sometimes.
I thought yours was an honest question that warrants an answer (which thankfully Chris answered).
ta8645 · 8h ago
But once an algorithm to drag the colours back in-gamut was applied, would the lost perceptual uniformity still be a problem practically speaking, with DCI-P3 monitors?
chrismorgan · 8h ago
Yes. I repeat: these colours are way outside gamut. Not just a little bit. P3 helps a little bit, Rec.2020 would help a fair bit more, but you’re still asking for a yellow that is about twice as vibrant as is possible.
the_af · 2h ago
Wow, I never thought about bright light red when thinking of undisplayable colors. It makes a lot of intuitive sense, thanks!
layer8 · 4h ago
The underlying problem is that the color space humans can see doesn’t have nice uniform linear boundaries. The larger your color space, the more relevant that issue actually becomes.
cubefox · 3h ago
> The red in that gradient is way darker than the rest of it.
It doesn't look significantly darker to me.
twhb · 8h ago
Great post!
Also check out oklch.com, I found it useful for building an intuition. Some stumbling blocks are that hues aren’t the same as HSL hues, and max chroma is different depending on hue and lightness. This isn’t a bug, but a reflection of human eyes and computer screens; the alternative, as in HSL, is a consistent max but inconsistent meaning.
Another very cool thing about CSS’s OKLCH is it’s a formula, so you can write things like oklch(from var(--accent) calc(l + .1) c h). Do note, though, that you’ll need either some color theory or fiddling to figure out your formulas, my programmer’s intuition told me lies like “a shadow is just a lightness change, not a hue change”.
Also, OKLCH gradients aren’t objectively best, they’re consistently colorful. When used with similar hues, not like the article’s example, they can look very nice, but it’s not realistic; if your goal is how light mixes, then you actually want XYZ. More: https://developer.mozilla.org/en-US/docs/Web/CSS/color_value....
Also, fun fact: the “ok” is actually just the word “ok”. The implication being that LCH was not OK, it had some bugs.
disconcision · 1h ago
OKLCH plus relative colors let me seriously reduce the amount of hardcoded colors from my style sheet:
> Another very cool thing about CSS’s OKLCH is it’s a formula
While it’s more useful for a perceptual color space, relative colors are supported for all CSS color spaces e.g.
background-color: rgb(from var(--base-color) calc(r - 76.5) g calc(b + 76.5));
fidotron · 5h ago
> In the example above, you can see that the OKLCH colors maintain consistent blueness across all of the shades, while in the HSL example, the lighter shades drift to purple and the darker ones muddy out towards grayish.
There is a very clear shift towards green in the OKLCH lightness value change example, enormously more so than any purple vibe in the HSL example.
Clearly being able to select colours of the same perceptual intensity has value, but some of the claims here as to the benefits are exaggerated.
throwaway0123_5 · 6m ago
I don't know much about the science of colors and I imagine this is going to be very subjective but I would at "worst" describe the rightmost OKLCH color as blue-green (but probably just "light blue"). Meanwhile the two rightmost HSL colors I would not describe as blue at all. Second from right I would call "light purple" and the rightmost honestly looks grey to me (which is weird because the caption says the darker HSL values "muddy out towards greyish" but the leftmost values for OKLCH and HSL both look pretty blue to me).
Also if I use the macOS app "Digital Color Meter" I get essentially the same green value for the rightmost OKLCH and HSL colors (226 and 227 for "display native values" and 228 and 227 for sRGB).
altairprime · 2h ago
You can see why by looking at the Hue chart for this color:
To increase brightness past the limit of the Hue band for the color, the rendered output color on a display shifts cyan due to the limited brightness range of a saturated blue in the Display P3 color space. OKLCH is, when varying brightness along a gradient, Saturation-invariant rather than Hue-invariant; whether that effect is desirable is a matter of aesthetic preference, but after decades of Hue-invariant desaturated web color, it’s certainly refreshing to have a choice about which compromised invariance to take.
Science recently invented a much-deeper blue LED than we have now, so I expect in a decade or two, whatever ends up succeeding Display P3 will be much more able to represent that gradient without cyan-shift, and all of the years of OKLCH gradients created before that time will end up showing a more accurate blue gradient with only the colorspace change. In the meantime? Do whatever’s aesthetically pleasing; there is no Right Answer in design :)
ps. One could argue that a post-OKLCH colorspace should not accept the binary decision of Hue or Saturation invariance, and instead should be Saturation-invariant to the display’s native limit and then transition smoothly to Hue-invariance at that threshold. I believe that’s a Difficult Problem in color profile specification terms, since it isn’t just pre-calculating the changeover threshold for all monitors (not to mention, do you change blue sooner or same as red, etc) but it’ll be a while longer before I’m versed enough in ICCv4 to explain that perception. It sure would make for an interesting experimental DisplayCAL target, though!
fidotron · 1h ago
> You can see why by looking at the Hue chart for this color
This misses the point: the example claims the hue isn't shifting, when it very clearly is. It's not a question of why.
altairprime · 1h ago
The hue isn’t shifting in OKLCH at all; also, it’s definitely shifting when OKLCH is rendered to Display P3 or sRGB. This is normal and expected behavior for colorspace gradients when rendered to device profiles? But I suspect I’m too close to the problem to see what’s not explained properly, apologies.
crazygringo · 2h ago
Agreed. The hue changes completely from blue to cyan.
If that's a correct implementation of OKLCH, then it's not something I would ever touch. Something seems to be deeply wrong with however they're calculating hue.
HSL/HSV have issues with perceptual lightness. But not with hues. The hue is constant and doesn't need any correction depending on saturation or lightness.
nojs · 1h ago
I think you do usually want to rotate the hue a bit when changing the lightness though. It’s a difficult thing to get right and one of the reasons the tailwind builtin colour palettes are so useful.
crazygringo · 1h ago
You don't. That's not something graphic designers ever do as compensation for perceptual uniformity.
I looked into it a bit more, and it turns out it's a result of OKLCH easily producing colors out of gamut, and then choosing to sacrifice hue accuracy for better saturation accuracy.
That's a fundamental design flaw if you ask me. Changing hue is completely unacceptable in my book.
rafram · 4h ago
There’s no green shift at all in that example on my display. Could your calibration be off?
fidotron · 3h ago
It's practically cyan, which is half way to green, not a lighter version of the blue to the left. This is on a MBP built in display.
This totally has uses but it is not, as claimed, "there is no hue or saturation drift" given the hue has shifted so much.
jibal · 2h ago
There certainly is ... run a color picker over it.
rafram · 1h ago
I opened the macOS Digital Color Meter and set it to "native values" mode. The second-to-last OKLCH swatch has a green component of 202, and the last has a green component of 226. The corresponding values in the HSL swatches are 203 and 227.
Aside from a few criticisms that others have already raised I think this is quite a nice introduction to OKLCH and how to use them in CSS.
With that out of the way, I'd like to go on a tangent here: can anyone explain the modern trend of not including publishing dates in blog articles? It stood out to me here in particular because the opening sentence said that "OKLCH is a newer color model" and the "newer" part of that sentence will get dated quicker than you think. The main site does mention a date, but limits it to "August 2025" so this seems like a conscious choice and I just don't get it.
I can't explain it, but undated articles are a serious problem. I don't know whether it's a modern trend ... how can one tell in the absence of dates? I've seen plenty of undated content that appears to be old.
On some blogs I can only tell the timeframe of the content from the timestamps on the comments ... but many blogs like the OP's don't support comments. I'm not likely to revisit them. (The blurb on the OP's main page is ironic ... rather than obsessing over the smallest details I see obsession over esthetics to the detriment of functionality.)
hackrmn · 7h ago
> can anyone explain the modern trend of not including publishing dates in blog articles?
In such cases, I usually try to see if the `Last-Modified` header served with the HTML document over HTTP, can be useful, but I conclude that often the same people who don't bother with dating their content -- you'd think they'd understand where the word _blog_ comes from, as in "[web]-log" where timestamps are paramount -- these same people don't know or care how HTTP works. Hint: the `Last-Modified` is the last modification time of the _resource_, in this case the actual HTML document. Just because your "backend" re-rendered the content because you didn't bother with setting up your server caching correctly, doesn't mean you should pretend it's a brand new content every day (which https://jakub.kr/components/oklch-colors does, unfortunately, so you won't know the timestamp from HTTP).
necovek · 5h ago
I would imagine this is rather to whatever "blog engine" is used instead of the conscious choice of the author (even if they knew what they desire and what would qork better, it might not be their priority).
kevin_thibedeau · 1h ago
SEO to protect old content from being demoted. It is annoying.
JohnKemeny · 9h ago
OKLCH: a color model based on OKLab (a perceptually uniform color space) where you control Lightness, Chroma (saturation), and Hue.
"OK" because "it does an ok job" according to its creater Björn Ottosson.
pavlov · 9h ago
He’s Swedish, so I bet OK is actually short for “Ottossons kulör” but he’s just being modest.
xg15 · 4h ago
In the spirit of "Oll Korrekt", "Otto's Kolors"?
How do you pronounce it, btw? "Oklich"? "okay L.C.H."?
pavlov · 3h ago
Lich is an old word for a corpse (or in D&D mythology an undead magician).
An okay lich is like a chill corpse, maybe?
xg15 · 37m ago
Was more thinking of a single word like "Oxford", but that works as well!
karmakaze · 3h ago
Why is there no documented formula to convert to from this color space? A quick google and the best I could find is this Gist[0]. Searching for Oklab has a Wikipedia page[1].
It looks to me that all the "magic" is in the matrices used for conversion between Oklab and sRGB. The final conversion between Oklab and Oklch is trivial, and is documented in your linked Wikipedia article.
dwringer · 2h ago
OKLCh is the same space as OKLab, it's just polar coordinates versus rectangular coordinates.
rollcat · 9h ago
Wherever you're working with colors and text/emblems, please also consider contrast and legibility: <https://apcacontrast.com/>
robin_reala · 9h ago
While the above site is great for measuring with a modern contrast algorithm (it’s the current algorithm for the yet-to-be-released WCAG 3 accessibility standards), it’s worth bearing in mind that the WCAG 2 algorithm is somewhat different, and a legal requirement in many markets / industries. You can check your colours against that with a tool like https://www.siegemedia.com/contrast-ratio, although there are many more.
Oh, interesting, I’d missed that. Good info, thanks!
seanwilson · 8h ago
You can pick colors that pass both APCA and WCAG contrast checks though so it's not a problem to use APCA recommendations now.
I find APCA is a little stricter than WCAG for light themes, and APCA is much stricter than WCAG for dark themes, to the point where you really shouldn't use WCAG for dark themes. So most of the time APCA is giving you stricter contrast that easily pass WCAG also.
I keep seeing mentions that APCA will let you finally use e.g. white on orange, or white on vibrant blue that pass APCA but fail on WCAG, but my feeling is there's not a lot of examples like this and most of these pairings only have okay contrast anyway, not great contrast, so it's not ideal to be stuck with WCAG's false negatives but not that big of a deal.
robin_reala · 8h ago
If your colours have enough contrast to pass them both then of course that’s fine!
I only bring it up because I had a situation last week where the better APCA was giving results for both white-on-colour and #111-on-colour as suitable for headline copy under WCAG3, but #111-on-colour was 7.5:1 and white-on-colour was 2.5:1 under WCAG2, hence we could only use one of them legally.
seanwilson · 8h ago
> I only bring it up because I had a situation last week where the better APCA was giving results for both white-on-colour and #111-on-colour as suitable for headline copy under WCAG3, but #111-on-colour was 7.5:1 and white-on-colour was 2.5:1 under WCAG2, hence we could only use one of them legally.
Yeah I understand, would you agree this is fairly rare when using APCA though?
I've had the opposite where the brand guide was suggesting we use a light on dark combo that passed WCAG2, yet it failed APCA, and worst of all clearly had poor contrast just by looking at it. Yet, some people will still go with it because WCAG2 gave it the okay haha.
robin_reala · 7h ago
Rare, yes. Checking with both is definitely recommended!
seanwilson · 7h ago
Maybe you've seen this but there's also https://github.com/Myndex/bridge-pca that does the "this color pair passes both APCA and WCAG2?" check in one pass.
cb321 · 4h ago
As per discussion of this new OKLCH idea in TFA - Are we even sure we have great formulas for measuring/defining contrast in the first place? Do you agree / disagree with any of the counterexamples over at: https://github.com/tattoy-org/contrast-experiments
seanwilson · 3h ago
I'm not following. These examples are using the WCAG2 contrast algorithm which is well known to be flawed for people interested in this stuff, especially for dark themes so there should be lots of bad examples here? APCA is supposed to improve on this (see the example graphic comparing WCAG2 and APCA): https://git.apcacontrast.com/documentation/WhyAPCA.html
> But as @c-blake has rightly pointed out, this doesn't take into account the ratio of visible background pixels to foreground pixels. For example the contrast required for a single fullstop character, ".", is goting to be diffrent from a capital, "B".
So APCA includes more guidance on font weight and font size for more contexts (e.g. headings, body text, shorter text, copyright notices), but it's still going to be an approximation for edge cases like displaying a single fullstop character. If this case is common, you'd want to increase the contrast value instead of going with the minimum passing value, so the contrast algorithms can still help you.
There's a tradeoff with having guidelines that are very accurate (e.g. a contrast algorithm that counts pixels) vs simpler to follow (e.g. recommended font weight and size). People already find WCAG2 hard to follow as it is.
cb321 · 2h ago
I don't think you & I have much disagreement here as I like the way you write about approximations and edge cases and things involving human judgement calls and "both not either" kinds of testing. The WhyAPCA document you link to also includes language to such effect with sliding scales over regions & such. Me - I'm mostly asking questions not offering answers. That said, to correct the record..
>These examples are using the WCAG2 contrast algorithm which is well known
Only one of the 4 tables shown is the thing you say is the known-to-be-flawed WCAG2 one. Some counterxamples are listed for all 4 formulas, though, 2 of which use the CIE Lightness (which, sure, is probably different, but I believe the CIE L is what APCA is based upon - in spite of so..many..words on their doc pages they often just say "lightness").
------------------------
Another point of those 4 tables, perhaps more clear when looking at the python script, is whether "numerical ratio" vs abs(difference) is better. It seems to me that color space designers, like this OKLCH, are going after "perceptual linearity" which suggests abs(diff) is far more appropriate than a "ratio" which has "near zero" troubles (and zero & one are downright seductive numbers for perceptual lightness scales).
I certainly should learn more about it, but various "click through" APCA things I've seen seem to speak in ratio terms like "10 times the contrast" (though admittedly that only assumes some scale for contrast not that it's formulated as a ratio - it's just suggestive). So, I should probably look more into it before actually offering a critique, but it still has the feeling of "cross purposes" - using some color space axis designed for [0,1] linearity differences instead for ratios within that axis. When I tried using the WCAG2 one I was kind of stunned how sensitive everything was to what should have been a kind of "arbitrary adjustment" to handle near-zero.
I might wonder what designers of color spaces actually have to say about this ratio vs. difference issue if you know of any articles. You seem knowledgeable. The spaces seem literally designed for differences to me.
I tried working with it but had to give it up for practical purposes. Whereas the focus with HSL is on the Lightness part and the Saturation is made to fit, OKHCL does it differently. It pushes the Chroma part to it's technical limits and abuses the Hue to make it fit, but we just do not understand Chroma intuitively.
I am waiting for OKHSL where the adjustments will bu much smaller and do not lead to absurd changes in intent.
I already had a discussion about it somewhere else (https://www.reddit.com/r/css/comments/1jv5f0r/hue_is_an_issu...)
once_inc · 6h ago
My mind immediately translated OKLCH into "Oklachroma".
Aissen · 8h ago
On the comparison between Color spaces, it's weird, my monitor from 2008 does show a difference between the Display-P3 and the sRGB purple colors, yet I didn't think it'd have such a big color range. Is there some color conversion at the browser or OS-level? (my distro/desktop enables colormgr by default).
chrismorgan · 8h ago
It’s just completely wrong.
The first uses oklch(0.65 0.20 300), comfortably inside sRGB, not even at the boundary. The second uses oklch(0.65 0.28 300), which is well outside P3 and even Rec.2020.
The smallest fix would be to make the second one oklch(0.65 0.2399 300) to bring it inside P3 so the demo doesn’t get slightly warped if Rec.2020-capable (not really necessary, but preferable, I’d say), and the first #a95eff (oklch(0.6447 0.2297 301.67)) which is CSS’s fallback.
But purple is also pretty much the worst choice for such a demo—P3 adds the least to sRGB around there, so the difference will be smallest. A better choice is red or green.
So a better pair would be oklch(0.65 0.2977284 28) on the right (a bright red at the very edge of the P3 gamut, well outside sRGB) and #f00 on the left (the sRGB value CSS will map it to if out of gamut).
ksec · 5h ago
Sort of off topic questions, do we have any upcoming colour space beyond BT2020, now that we soon have monitor that reach 100% BT2020. I did some search and it doesn't seems to be any.
adrian_b · 4h ago
For any really bigger color space, you would have to use more than 3 primary colors, which would increase a lot the cost.
Moving the monochromatic BT.2020 colors from 630 nm, 532 nm and 467 nm could get a little increase in color space coverage, but at the expense of a lower efficiency in power consumption to brightness conversion. 467 nm is not a very pure blue, but the sensitivity of the eye drops very quickly in the blue region, so a better blue would require much more power. Similarly, though not so pronounced, for a different green.
Moreover, in the green region there is a gap, both for lasers and for LEDs, where the available devices have low efficiencies for converting electrical power to light, so changing the frequency of the primary green color would have to take that into account too.
In conclusion, I believe that the BT.2020 (actually BT.2100) color space is close to the best that can be done in displays of reasonable price and energy efficiency.
A true coverage of 100% of the BT.2100 color space can be realized only with laser projectors. Any display with LEDs or quantum dots will never have really monochromatic primary colors, though a coverage of significantly more than 90% of the BT.2100 color space is not too difficult. However, the advertised percentage of the color space may be misleading, because it varies depending on the kind of color space used for computations. A coverage percentage computed in OKlab would be more informative than a percentage computed in the XYZ color space.
guenthert · 3h ago
> For any really bigger color space, you would have to use more than 3 primary colors, which would increase a lot the cost.
Unless you want to make displays for the bees and birds (and the tiny alleged minority of human tetrachromats) that seems rather pointless. People with three color receptors are your customers, so that's driving the market.
I rather predict, future displays will further improve on contrast, including very bright (brilliant) sparks. Imagine an iPhone glittering like gold or diamonds ...
adrian_b · 1h ago
This has nothing to do with tetrachromatism.
The border of the color space corresponding to monochromatic colors is convex, so any triangle inscribed in that curve border will leave parts of the color space that cannot be reproduced on a display.
The convexity of the border means that if you compute the 3 coefficients of RGB colors that match a desired color, there will always be some colors that need one negative coefficient, regardless of the choice for the RGB primary colors. On any display, it is impossible to realize a negative brightness of a color, so on a RGB display there will always be some colors whose hue and brightness can be reproduced, but their saturation cannot be reproduced.
The only way to make smaller the parts of the color space that cannot be reproduced is to take more points on the monochromatic border, replacing the triangle of reproducible colors with a polygon that fits more closely the curved border.
The entire color space perceived by humans could be reproduced on a display only with tunable lasers, not with fixed-frequency primary colors. One could use fixed-frequency primary colors only if they would stimulate directly the photoreceptors in the eye, to enable workarounds for the overlapping filter characteristics of the cones and for the signal processing done in the retina.
hansvm · 24m ago
That's not the issue. Take pure blue wavelengths as an example. They also activate your green cones a little. Increasing the frequency activates the blue cones less and the green cones much less, yielding a higher ratio of blue to green activation, and a new color (violet) that you can't represent with mixed color output exactly aligning with mode receptor wavelengths.
ksec · 3h ago
>Any display with LEDs or quantum dots will never have really monochromatic primary colors
I was referring to the new RGB LED. From what I have read so far seems to be doing far better than LED or quantum dots.
But I guess we will have to settle with BT2100 then.
jakubkrehel · 3h ago
This should be fixed now as well!
jedimastert · 1h ago
For historical "neat" factor, here's the original blog post that introduced the color space:
Nice post. OKLCH is quite handy but for writing colors in CSS I hope eventually we’ll get some form of OKHSL/OKHSV[1] so users don’t need to worry about gamut boundaries.
There is a youtuber (Gneiss Name) making educational content through the medium of Minecraft.
He's made one on OKLab as well: https://youtu.be/nJlZT5AE9zY
jedimastert · 1h ago
What an absolutely fascinating channel! Thanks for the link
MontagFTB · 3h ago
> The way gradients work in OKLCH is pretty different compared to sRGB. In sRGB, gradients are calculated in red, green, and blue values, which often leads to muddy midpoints and uneven brightness.
I always understood those “muddy midpoints” as a failure to properly gamma correct the interpolation between two (s)RGB colors. Is that happening here, or is the mud coming from something else?
kevin_thibedeau · 1h ago
Grays run along a diagonal axis of the RGB cube after stripping gamma off. A straight line through the cube will brush by it. This is enhanced when transitioning from a primary (green) to an opposite corner (magenta).
adornKey · 3h ago
The best axis for Lightness in my opinion is still the Gray-Scale (as used back in the day for black/white/grayscale TVs).
The newer CIE colorspaces (CIECAM02 CIECAM16) seem to address the effect, that color-perception goes wild if you change background and illumination. Oklab seems to only make some fixed choice about how to include the chromatic part to lightness. I'm not so sure, how this definition of lightness is any better than grayscale (from 1931).
I've not touched oklch, but I've played with oklab gradients a fair amount.
How do they (oklch & oklab) compare for different uses?
tovej · 9h ago
oklch uses the oklab color space.
cluckindan · 8h ago
The oklch color space is polar: it’s a cylindrical transformation of the oklab cartesian color space.
raincole · 7h ago
That's quite misleading. The parent commenter was asking about gradient (interpolation between colors). Gradients look completely different in oklch and oklab.
tovej · 7h ago
Well yes, it's a different coorsinate system, so gradients would look different. It is still the same color space, but I agree I could have worded that better.
Does anyone know how this is different to the Munsell color space, which is also perceptually uniform?
Edit: I would imagine that the only way to definine a perceptually uniform color space is by tons of user testing. This is how Munsell developed his color space… specifically presenting test subjects with pairs of identical and near-identical color swatches and asking if they could tell the difference.
In this way, pairwise comparisom of similararity became the bedrock of color perception science.
shinze · 2h ago
Oklch is open source and part of the web standard, Munsell colors probably needs a licence to be used ?
DeusExMachina · 4h ago
My understanding is that it's the same with higher resolution.
tiedemann · 9h ago
Seems nice. But how to pronounce it?
rollcat · 9h ago
That's one reason to prefer Oklab ;)
Etheryte · 9h ago
With great difficulty.
idle_zealot · 9h ago
Like "okay lock" I would guess.
thiht · 7h ago
o k l c h
BrenBarn · 8h ago
"Oh, clutch"?
skylurk · 9h ago
In the chromaticity diagram, is my Display-P3 screen mapping everything outside the triangle back into the triangle?
jonnybarnes · 9h ago
Yes, the diagram is a representation. Kind off like drawing 3D shapes on a 2D surface.
TiredOfLife · 8h ago
That gradient example is hilarious.
With RGB you order green salad you get green salad.
With OKLCH you order green salad you get beet soup.
jibal · 1h ago
Yes ... see chrismorgan's comment on it up top.
seanwilson · 9h ago
> It also works the other way around, where you can change the lightness value to create various color shades and there is no hue or saturation drift unlike in other color modes.
> In the example above, you can see that the OKLCH colors maintain consistent blueness across all of the shades, while in the HSL example, the lighter shades drift to purple and the darker ones muddy out towards grayish.
I see lots of automatic palette generator projects where the shades of each color are generated with OKLCH by only varying the lightness value on some chosen base color. The problem I find is if you look at popular open source palettes, the way the hand-crafted hue and saturation values vary across the shades for different hues isn't that predictable (the curve of the hue/saturation values over shades aren't straight lines or typical easing curves).
Hawking my own tool (using HSLuv with RGB for now), but you can load and compare the hue and saturation curves as they vary over shades of a color using example palettes from Tailwind 3, USWDS and IBM Carbon, plus tweak each shade to your liking:
So I think OKLCH is a nice starting base for palettes and a quick way to generate a color you need in CSS, but I think designers will always need to tweak the hue and saturation of each shade so it looks just right as there's no single right answer you could encode into the color space.
Hi Alexei, thanks for your work on HSLuv! I love the simplicity of it, where you can use HSLuv as mostly a drop-in replacement for HSL which most designers are familiar with.
I keep seeing new tutorials on designing accessible palettes that still use HSL, where the WCAG2 contrast breaks and goes all over the place as you vary the hue and saturation. HSLuv makes life so much easier here and lets you focus on exploring colors that you know will pass, using a familiar looking color picker.
lenkite · 2h ago
This. oklch requires you to be some sort of expert sage. HSLuv is so easy to grok.
letmeinhere · 5h ago
How does oklch compare to CIELCh(uv)? I've been using that seemingly similar system to pick uniform colors.
jedimastert · 1h ago
Here's the original post explaining the color space. The ideas are very similar, OKLAB used a different white point
Thanks for this post. Hackernews is sometimes awesome for learning opportunities like this. Never heard of the model, thankful for the article.
tzury · 5h ago
Quote:
colors are much more accurate in terms of
how humans perceive them and it makes
working with them much easier
This is an aim, which I am not sure fully addressed.
Think of the reason why can't I get oklch or any other method of color definition in HTML to produce the "gold color" as we humans think of it.
The fundamental reason you can't get a truly convincing "gold" color using a single value in oklch, rgb, or any other color definition is because gold is a material, not a color.
What our brain perceives as "gold" is not a single, flat hue.
It's a complex interplay of light, reflection, and texture.
Point is, even with sophisticated CSS involved with linear gradient it is still a challenge
<style>
.flat-gold {
width: 200px;
height: 200px;
/* Using Oklch for a perceptually uniform yellow */
background: oklch(85% 0.11 85);
}
.gradient-gold {
width: 200px;
height: 200px;
background: linear-gradient(
135deg,
oklch(60% 0.1 65), /* Dark, desaturated shadow (brownish) */
oklch(85% 0.11 85) 45%, /* Rich mid-tone gold */
oklch(98% 0.1 90) 50%, /* Sharp, bright highlight (almost white-yellow) */
oklch(85% 0.11 85) 55%, /* Back to the mid-tone */
oklch(70% 0.1 75) /* Softer shadow on the other side */
);
}
.conic-gold {
width: 200px;
height: 200px;
border-radius: 50%; /* Often looks best on a circle */
background: conic-gradient(
from 90deg,
#B38728, /* Darker Start */
#FEE9A0, /* Bright Highlight */
#D4AF37, /* Mid-tone */
#FEE9A0, /* Another Highlight */
#B38728 /* Darker End */
);
}
.premium-gold {
width: 200px;
height: 200px;
background-color: #B38728; /* Fallback color */
background-image:
/* Layer 1: Sharp highlight on top */
linear-gradient(
175deg,
rgba(255, 253, 240, 0.6) 0%,
rgba(255, 215, 0, 0.2) 40%,
rgba(136, 96, 0, 0.5) 90%
),
/* Layer 2: Base metallic gradient */
linear-gradient(
105deg,
transparent 35%,
#FEE9A0 48%,
#D4AF37 52%,
transparent 65%
);
border: 2px solid oklch(60% 0.1 65);
box-shadow: inset 0 0 10px rgba(0,0,0,0.4);
}
</style>
<div class="flat-gold"></div>
<hr />
<div class="gradient-gold"></div>
<hr />
<div class="conic-gold"></div>
<hr />
<div class="premium-gold"></div>
tovej · 9h ago
Really happy about oklch. You do have to learn the hue numbers, but once you do, everything is more intuitive.
dev_l1x_be · 8h ago
I was wondering about this exact subject the other day when working on some web dev task. Now I know why this way is better.
lieblingautor · 9h ago
seems like a great idea, this will make working with colors so much easier
CIAOBENGA · 9h ago
Awesome Post
snvzz · 2h ago
HSV with extra steps?
teekert · 8h ago
These IP addresses being released at some point, and making their way into something else is probably the reason I never got to fully run my mailserver from my basement. These companies are just massively giving IP addresses a bad reputation, messing them up for any other use and then abandoning them. I wonder what this would look like when plotted: AI (and other toxic crawling) companies slowly consuming the IPv4 address space? Ideally we'd forced them into some corner of the IPv6 space I guess. I mean robots.txt seems not to be of any help here.
OKLCH is a polar coordinate space. Hue is angle in this space. So to interpolate hue from one angle to another, to get from one side of a circle to the other, you go round the edge. This leads to extreme examples like the one shown:
You can also go round the circle the other way, which will take you via blue–aqua instead of via red–yellow: The gradient shown (in either case) is a good example of a way that perceptual colour spaces are really bad to work in: practically the entire way round the edge of the circle, it’s outside sRGB, in fact way outside of the colours humans can perceive. Perceptual colour spaces are really bad at handling the edges of gamuts, where slightly perturbing the values take you out of gamut.Accordingly, there are algorithms defined (yes, plural: not every application has agreed on the technique to use) to drag the colour back in-gamut, but it sacrifices the perceptual uniformity. The red in that gradient is way darker than the rest of it.
When you’re looking for better gradients, if you’re caring about perceptual uniformity (which frequently you shouldn’t, perceptual colour spaces are being massively overapplied), you should probably default to interpolating in Oklab instead, which takes a straight line from one side of the circle to the other—yes, through grey, if necessary.
And in this case, that gets you about as decent a magenta-to-lime gradient as you can hope for, not going via red and yellow, and not exhibiting the inappropriate darkening of sRGB interpolation (… though if I were hand-tuning such a gradient, I’d actually go a bit darker than Oklab does).During its beta period, Tailwind v4 tried shifting from sRGB to Oklch for gradient interpolation; by release, they’d decided Oklab was a safer default.
Which brings me to point at the crux of the matter: avoid gradients between two dissimilar colors in the first place.
Usually you fix it by moving your point through a different colour space. Choice depends on your requirements and mediums you're working with (normally different types of light sources or screens).
I had to write a low level colour interpolation librar for a few interactive art projects, so I dipped a bit into this, but I'm no colour expert
Failure to do this conversion is what leads to the bad results when interpolating: going from red to green will still go through grey but it should go through a much lighter grey compared to what happens if you get the interpolation wrong.
[EDIT] Ahh.. The W3C has already looked at this. https://www.w3.org/Graphics/Color/Workshop/slides/talk/lille...
See slide 19: https://www.w3.org/Graphics/Color/Workshop/slides/talk/lille... -- if you ask CIELAB to make "pure blue" (RGB 0 0 100%) become grayscale, the intermediate colors become purple to the human eye. The entire point of a perceptual color space is that that doesn't happen. OKLCH fixes that.
BTW, credit to Björn Ottosson, who basically side-projected a color space into the web standards and more: https://bottosson.github.io/posts/oklab/ ... folks like him are why we sometimes have nice things!
Isn't it any continuous function that starts at a specified color and ends at another specified color?
How then does one say that any gradient is good or bad?
Isn't the problem you are highlighting guaranteed to exist for any colorspace that defines colors outside of human perception?
It’s a “color” because it’s useful to describe such a thing. If you had monitor entirely filled with 50% white you’d call it white. Only by comparing it to something brighter do you call it gray. Brown is the same thing. In a dark room if you looked at a monitor filled with red and green pixels you’d call it orange. Only when you start adding in clues like whites and brighter colors would you call it brown.
Anyway, yes grey is a color. But it is not quite the same as other colors. Other colors occupy only parts of the visible electromagnetic spectrum. Whites are the whole thing.
There is actually several very good technology connections videos about this stuff. Color is very cool!
So, depending on what you're doing, you want different things. You may want to view your color space as an RGB cube, and go through gray. Or you may want to view your color space as something more like HLS or OKLCH, and not go through gray.
And yes, both oklch gradients look pretty weird while the oklab gradient looks nice (if you can accept it going through grey).
For this specific gradient, see https://oklch.com/#0.7017,0.3225,328.36,100 and https://oklch.com/#0.86644,0.294827,142.4953,100, and look at the Chroma panel, see how far out of our screen gamuts they are (even tick “Show Rec2020”, which adds a lot of chroma around blue–green and magenta–red), and try to imagine the colours between the lime and magenta (in either direction). The red direction is probably the easier to reason about: there’s just no such colour as a light, bright red. You can have bright or light, but not both. (Its 3D view can also be useful to visualise these things: you’re building a straight-line bridge between two peaks, and there’s a chasm in between.)
edit: Also, you mentioned the colors "beyond the ranges of human perception" but I don't think there is any such limitation here, the bottleneck is the hardware (computer monitors).
I thought yours was an honest question that warrants an answer (which thankfully Chris answered).
It doesn't look significantly darker to me.
Also check out oklch.com, I found it useful for building an intuition. Some stumbling blocks are that hues aren’t the same as HSL hues, and max chroma is different depending on hue and lightness. This isn’t a bug, but a reflection of human eyes and computer screens; the alternative, as in HSL, is a consistent max but inconsistent meaning.
Another very cool thing about CSS’s OKLCH is it’s a formula, so you can write things like oklch(from var(--accent) calc(l + .1) c h). Do note, though, that you’ll need either some color theory or fiddling to figure out your formulas, my programmer’s intuition told me lies like “a shadow is just a lightness change, not a hue change”.
Also, OKLCH gradients aren’t objectively best, they’re consistently colorful. When used with similar hues, not like the article’s example, they can look very nice, but it’s not realistic; if your goal is how light mixes, then you actually want XYZ. More: https://developer.mozilla.org/en-US/docs/Web/CSS/color_value....
Also, fun fact: the “ok” is actually just the word “ok”. The implication being that LCH was not OK, it had some bugs.
https://github.com/hazelgrove/hazel/blob/dev/src/web/www/sty...
While it’s more useful for a perceptual color space, relative colors are supported for all CSS color spaces e.g.
There is a very clear shift towards green in the OKLCH lightness value change example, enormously more so than any purple vibe in the HSL example.
Clearly being able to select colours of the same perceptual intensity has value, but some of the claims here as to the benefits are exaggerated.
Also if I use the macOS app "Digital Color Meter" I get essentially the same green value for the rightmost OKLCH and HSL colors (226 and 227 for "display native values" and 228 and 227 for sRGB).
https://oklch.com/#0.7684,0.1754,218.1,100
To increase brightness past the limit of the Hue band for the color, the rendered output color on a display shifts cyan due to the limited brightness range of a saturated blue in the Display P3 color space. OKLCH is, when varying brightness along a gradient, Saturation-invariant rather than Hue-invariant; whether that effect is desirable is a matter of aesthetic preference, but after decades of Hue-invariant desaturated web color, it’s certainly refreshing to have a choice about which compromised invariance to take.
https://news.ycombinator.com/item?id=44588388
Science recently invented a much-deeper blue LED than we have now, so I expect in a decade or two, whatever ends up succeeding Display P3 will be much more able to represent that gradient without cyan-shift, and all of the years of OKLCH gradients created before that time will end up showing a more accurate blue gradient with only the colorspace change. In the meantime? Do whatever’s aesthetically pleasing; there is no Right Answer in design :)
ps. One could argue that a post-OKLCH colorspace should not accept the binary decision of Hue or Saturation invariance, and instead should be Saturation-invariant to the display’s native limit and then transition smoothly to Hue-invariance at that threshold. I believe that’s a Difficult Problem in color profile specification terms, since it isn’t just pre-calculating the changeover threshold for all monitors (not to mention, do you change blue sooner or same as red, etc) but it’ll be a while longer before I’m versed enough in ICCv4 to explain that perception. It sure would make for an interesting experimental DisplayCAL target, though!
This misses the point: the example claims the hue isn't shifting, when it very clearly is. It's not a question of why.
If that's a correct implementation of OKLCH, then it's not something I would ever touch. Something seems to be deeply wrong with however they're calculating hue.
HSL/HSV have issues with perceptual lightness. But not with hues. The hue is constant and doesn't need any correction depending on saturation or lightness.
I looked into it a bit more, and it turns out it's a result of OKLCH easily producing colors out of gamut, and then choosing to sacrifice hue accuracy for better saturation accuracy.
That's a fundamental design flaw if you ask me. Changing hue is completely unacceptable in my book.
This totally has uses but it is not, as claimed, "there is no hue or saturation drift" given the hue has shifted so much.
Basically no difference at all.
https://evilmartians.com/chronicles/oklch-in-css-why-quit-rg...
Along with their picker / converter here:
https://oklch.com/
Discussed on Hacker News here:
https://news.ycombinator.com/item?id=43073819 (6 months ago, 30 comments)
With that out of the way, I'd like to go on a tangent here: can anyone explain the modern trend of not including publishing dates in blog articles? It stood out to me here in particular because the opening sentence said that "OKLCH is a newer color model" and the "newer" part of that sentence will get dated quicker than you think. The main site does mention a date, but limits it to "August 2025" so this seems like a conscious choice and I just don't get it.
[0] https://jakub.kr/
On some blogs I can only tell the timeframe of the content from the timestamps on the comments ... but many blogs like the OP's don't support comments. I'm not likely to revisit them. (The blurb on the OP's main page is ironic ... rather than obsessing over the smallest details I see obsession over esthetics to the detriment of functionality.)
In such cases, I usually try to see if the `Last-Modified` header served with the HTML document over HTTP, can be useful, but I conclude that often the same people who don't bother with dating their content -- you'd think they'd understand where the word _blog_ comes from, as in "[web]-log" where timestamps are paramount -- these same people don't know or care how HTTP works. Hint: the `Last-Modified` is the last modification time of the _resource_, in this case the actual HTML document. Just because your "backend" re-rendered the content because you didn't bother with setting up your server caching correctly, doesn't mean you should pretend it's a brand new content every day (which https://jakub.kr/components/oklch-colors does, unfortunately, so you won't know the timestamp from HTTP).
"OK" because "it does an ok job" according to its creater Björn Ottosson.
How do you pronounce it, btw? "Oklich"? "okay L.C.H."?
An okay lich is like a chill corpse, maybe?
[0] https://gist.github.com/dkaraush/65d19d61396f5f3cd8ba7d1b4b3...
[1] https://en.wikipedia.org/wiki/Oklab_color_space
I am not sure what the status is.
I find APCA is a little stricter than WCAG for light themes, and APCA is much stricter than WCAG for dark themes, to the point where you really shouldn't use WCAG for dark themes. So most of the time APCA is giving you stricter contrast that easily pass WCAG also.
I keep seeing mentions that APCA will let you finally use e.g. white on orange, or white on vibrant blue that pass APCA but fail on WCAG, but my feeling is there's not a lot of examples like this and most of these pairings only have okay contrast anyway, not great contrast, so it's not ideal to be stuck with WCAG's false negatives but not that big of a deal.
I only bring it up because I had a situation last week where the better APCA was giving results for both white-on-colour and #111-on-colour as suitable for headline copy under WCAG3, but #111-on-colour was 7.5:1 and white-on-colour was 2.5:1 under WCAG2, hence we could only use one of them legally.
Yeah I understand, would you agree this is fairly rare when using APCA though?
I've had the opposite where the brand guide was suggesting we use a light on dark combo that passed WCAG2, yet it failed APCA, and worst of all clearly had poor contrast just by looking at it. Yet, some people will still go with it because WCAG2 gave it the okay haha.
> But as @c-blake has rightly pointed out, this doesn't take into account the ratio of visible background pixels to foreground pixels. For example the contrast required for a single fullstop character, ".", is goting to be diffrent from a capital, "B".
So APCA includes more guidance on font weight and font size for more contexts (e.g. headings, body text, shorter text, copyright notices), but it's still going to be an approximation for edge cases like displaying a single fullstop character. If this case is common, you'd want to increase the contrast value instead of going with the minimum passing value, so the contrast algorithms can still help you.
There's a tradeoff with having guidelines that are very accurate (e.g. a contrast algorithm that counts pixels) vs simpler to follow (e.g. recommended font weight and size). People already find WCAG2 hard to follow as it is.
>These examples are using the WCAG2 contrast algorithm which is well known
Only one of the 4 tables shown is the thing you say is the known-to-be-flawed WCAG2 one. Some counterxamples are listed for all 4 formulas, though, 2 of which use the CIE Lightness (which, sure, is probably different, but I believe the CIE L is what APCA is based upon - in spite of so..many..words on their doc pages they often just say "lightness").
------------------------
Another point of those 4 tables, perhaps more clear when looking at the python script, is whether "numerical ratio" vs abs(difference) is better. It seems to me that color space designers, like this OKLCH, are going after "perceptual linearity" which suggests abs(diff) is far more appropriate than a "ratio" which has "near zero" troubles (and zero & one are downright seductive numbers for perceptual lightness scales).
I certainly should learn more about it, but various "click through" APCA things I've seen seem to speak in ratio terms like "10 times the contrast" (though admittedly that only assumes some scale for contrast not that it's formulated as a ratio - it's just suggestive). So, I should probably look more into it before actually offering a critique, but it still has the feeling of "cross purposes" - using some color space axis designed for [0,1] linearity differences instead for ratios within that axis. When I tried using the WCAG2 one I was kind of stunned how sensitive everything was to what should have been a kind of "arbitrary adjustment" to handle near-zero.
I might wonder what designers of color spaces actually have to say about this ratio vs. difference issue if you know of any articles. You seem knowledgeable. The spaces seem literally designed for differences to me.
The first uses oklch(0.65 0.20 300), comfortably inside sRGB, not even at the boundary. The second uses oklch(0.65 0.28 300), which is well outside P3 and even Rec.2020.
The smallest fix would be to make the second one oklch(0.65 0.2399 300) to bring it inside P3 so the demo doesn’t get slightly warped if Rec.2020-capable (not really necessary, but preferable, I’d say), and the first #a95eff (oklch(0.6447 0.2297 301.67)) which is CSS’s fallback.
But purple is also pretty much the worst choice for such a demo—P3 adds the least to sRGB around there, so the difference will be smallest. A better choice is red or green.
So a better pair would be oklch(0.65 0.2977284 28) on the right (a bright red at the very edge of the P3 gamut, well outside sRGB) and #f00 on the left (the sRGB value CSS will map it to if out of gamut).
Moving the monochromatic BT.2020 colors from 630 nm, 532 nm and 467 nm could get a little increase in color space coverage, but at the expense of a lower efficiency in power consumption to brightness conversion. 467 nm is not a very pure blue, but the sensitivity of the eye drops very quickly in the blue region, so a better blue would require much more power. Similarly, though not so pronounced, for a different green.
Moreover, in the green region there is a gap, both for lasers and for LEDs, where the available devices have low efficiencies for converting electrical power to light, so changing the frequency of the primary green color would have to take that into account too.
In conclusion, I believe that the BT.2020 (actually BT.2100) color space is close to the best that can be done in displays of reasonable price and energy efficiency.
A true coverage of 100% of the BT.2100 color space can be realized only with laser projectors. Any display with LEDs or quantum dots will never have really monochromatic primary colors, though a coverage of significantly more than 90% of the BT.2100 color space is not too difficult. However, the advertised percentage of the color space may be misleading, because it varies depending on the kind of color space used for computations. A coverage percentage computed in OKlab would be more informative than a percentage computed in the XYZ color space.
Unless you want to make displays for the bees and birds (and the tiny alleged minority of human tetrachromats) that seems rather pointless. People with three color receptors are your customers, so that's driving the market.
I rather predict, future displays will further improve on contrast, including very bright (brilliant) sparks. Imagine an iPhone glittering like gold or diamonds ...
The border of the color space corresponding to monochromatic colors is convex, so any triangle inscribed in that curve border will leave parts of the color space that cannot be reproduced on a display.
The convexity of the border means that if you compute the 3 coefficients of RGB colors that match a desired color, there will always be some colors that need one negative coefficient, regardless of the choice for the RGB primary colors. On any display, it is impossible to realize a negative brightness of a color, so on a RGB display there will always be some colors whose hue and brightness can be reproduced, but their saturation cannot be reproduced.
The only way to make smaller the parts of the color space that cannot be reproduced is to take more points on the monochromatic border, replacing the triangle of reproducible colors with a polygon that fits more closely the curved border.
The entire color space perceived by humans could be reproduced on a display only with tunable lasers, not with fixed-frequency primary colors. One could use fixed-frequency primary colors only if they would stimulate directly the photoreceptors in the eye, to enable workarounds for the overlapping filter characteristics of the cones and for the signal processing done in the retina.
I was referring to the new RGB LED. From what I have read so far seems to be doing far better than LED or quantum dots.
But I guess we will have to settle with BT2100 then.
https://bottosson.github.io/posts/oklab/
[1] https://bottosson.github.io/posts/colorpicker/
I always understood those “muddy midpoints” as a failure to properly gamma correct the interpolation between two (s)RGB colors. Is that happening here, or is the mud coming from something else?
The newer CIE colorspaces (CIECAM02 CIECAM16) seem to address the effect, that color-perception goes wild if you change background and illumination. Oklab seems to only make some fixed choice about how to include the chromatic part to lightness. I'm not so sure, how this definition of lightness is any better than grayscale (from 1931).
https://apps.apple.com/us/app/cone-color-picker-identifier/i...
https://sindresorhus.com/system-color-picker
https://evilmartians.com/opensource/oklch-color-picker
https://oklch.eerolehtinen.fi/
https://github.com/eero-lehtinen/oklch-color-picker
How do they (oklch & oklab) compare for different uses?
https://bottosson.github.io/posts/oklab/
Edit: I would imagine that the only way to definine a perceptually uniform color space is by tons of user testing. This is how Munsell developed his color space… specifically presenting test subjects with pairs of identical and near-identical color swatches and asking if they could tell the difference.
In this way, pairwise comparisom of similararity became the bedrock of color perception science.
With RGB you order green salad you get green salad.
With OKLCH you order green salad you get beet soup.
> In the example above, you can see that the OKLCH colors maintain consistent blueness across all of the shades, while in the HSL example, the lighter shades drift to purple and the darker ones muddy out towards grayish.
I see lots of automatic palette generator projects where the shades of each color are generated with OKLCH by only varying the lightness value on some chosen base color. The problem I find is if you look at popular open source palettes, the way the hand-crafted hue and saturation values vary across the shades for different hues isn't that predictable (the curve of the hue/saturation values over shades aren't straight lines or typical easing curves).
Hawking my own tool (using HSLuv with RGB for now), but you can load and compare the hue and saturation curves as they vary over shades of a color using example palettes from Tailwind 3, USWDS and IBM Carbon, plus tweak each shade to your liking:
https://www.inclusivecolors.com/?style_dictionary=eyJjb2xvci...
So I think OKLCH is a nice starting base for palettes and a quick way to generate a color you need in CSS, but I think designers will always need to tweak the hue and saturation of each shade so it looks just right as there's no single right answer you could encode into the color space.
I keep seeing new tutorials on designing accessible palettes that still use HSL, where the WCAG2 contrast breaks and goes all over the place as you vary the hue and saturation. HSLuv makes life so much easier here and lets you focus on exploring colors that you know will pass, using a familiar looking color picker.
https://bottosson.github.io/posts/oklab/#what-about-existing...
The fundamental reason you can't get a truly convincing "gold" color using a single value in oklch, rgb, or any other color definition is because gold is a material, not a color.
What our brain perceives as "gold" is not a single, flat hue. It's a complex interplay of light, reflection, and texture.
Point is, even with sophisticated CSS involved with linear gradient it is still a challenge
See demo at https://jsfiddle.net/oyw9fjda/
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Apologies! (I can't delete the post though, feel free to down-vote into oblivion)