I made a video tutorial about a similar thing long time ago - choosing black or white for text color given a color background. My solution was very simplistic. I just transformed the color to gray scale and compared it between black and white. It was a fun project. I'm not good making videos though.
>But, on a large project, with a large team, carefully managing such details can become a really hard task to get right. Suddenly a dark button has unreadable black text, and users can’t figure out what to do.
Cant someone take a look at the buttons before the large project ships? Alternatively make it mandatory to never have black text on a dark button and tell every team member including the large ones.
Interesting to read about the perceptual contrast vs mathematical - I did not know that. Going to integrate that into my workflow.
johnisgood · 1h ago
You may want to read about APCA, as you can have perceptual contrast calculations using the APCA algorithm.
refulgentis · 1h ago
You can have them with WCAG2, the stock APCA example hides the ball significantly and leads to a lot of incorrect conclusions in the article (tl;dr: black has more contrast by either measure, its just that APCA says you don't need as much contrast, so you can use white and have sufficient contrast)
johnisgood · 1h ago
I know about WCAG, too. You can also just implement a function that detects whether or not a color is dark or not. It is a general purpose function, e.g. my "isDark" function is: "func() < 0.5" (func() is omitted, but it is an algorithm). You can have "isLight", too, by doing "> 0.5". There are many ways to do this. You can just simply convert a hex color to RGB, then compute the luminance of the color, and then compare the luminance to a threshold (e.g. 0.5) to classify it as dark or light. The luminance function (WCAG luminance formula) converts RGB values to the range 0-1, applies gamma correction, and calculates luminance using the weighted sum of the gamma-corrected RGB values.
> APCA says you don't need as much contrast
You can always specify the threshold if you want, e.g. "apcaContrast(color)) >= $targetContrast" after adjusting, depending on what you want to do.
It really is easy, just make sure you have enough color space.
refulgentis · 54m ago
The WCAG luminance formula (relative luminance in color science terms) has perceptual mid gray at 0.18, not 0.5.
re: just change APCA contrast target, that's separate from the Not Even Wrong stuff in the article. I didn't mean to imply APCA is wrong to say you need less contrast, but rather, that the article is wrong to conclude white has more contrast.
johnisgood · 7m ago
Well, I used 0.5 as a convenient and intuitive midpoint of the 0-1 luminance range, but this of course is a simplification and doesn't align with human perception, it was more of an example if anything.
You are right, 0.18 is indeed perceptually closer to "middle gray" because the eye responds more sensitively to darker tones, so yeah, using a threshold closer to 0.18 makes more sense if we want to identify whether a color "feels" light or dark.
That said, 0.5 is a mathematical midpoint, but as I said, not aligned with how humans perceive brightness.
Ultimately one could use 0.18-0.3 as threshold.
jbritton · 1h ago
At a minimum it would be nice to know good colors for the pseudo classes active, focus, hover, link, visited and their various combinations for a light and dark theme. Additionally material UI adds disabled, before, after.
politelemon · 1h ago
I'm still not convinced that the contrasting colour should be the browser vendor's decision, it won't always be right or predictable. Will this be a definitive deterministic standard across all browsers? Instead this function feels like a tool to help UX teams during design phase.
MBCook · 54m ago
> Will this be a definitive deterministic standard across all browsers?
The article says the standard specifies the calculation to use.
Consistent, it is not. Ex. we can imagine a background at L* 50 that is ~equally served with a white or black foreground - in that case, the aesthetic principles come into play.
To also disambiguate that, and get to 100% reliable, if both a darker and lighter color are available given contrast K and background color C, look at C, if it's L* is >= 60, choose lighter.
Then, it is 100% correct and consistent.
dp-hackernews · 1h ago
Surely the relative colour theory colour wheel is the answer to this problem.
>This browser does not support contrast-color(). Try this demo in a browser that does, like Safari Technology Preview
ctippett · 1h ago
You don't need the Technology Preview, it's available as a WebKit Feature Flag under the advanced settings of normal Safari. I just enabled it on my phone and was able to view the demos.
judah · 2h ago
And I don't yet see an entry for this on caniuse.com. I'm guessing this is super new.
miiiiiike · 1h ago
Very new. I think Safari is the only one that ships it and even then it’s still in preview
homebrewer · 1h ago
It works in "Gnome Web", which is mostly a wrapper around WebKit.
> Support for this feature first shipped in March 2021, in Safari Technology Preview 122.
- The white on blue clearly has less contrast, not more. (squinting is a cheap way to test, or, walking backwards from your monitor)
With APCA, backgrounds around L* 60 tend to still allow white foregrounds, which is aesthetically closer to what the eye wants.
A black foreground would have more contrast regardless, even by APCA.
To be fair, this is how APCA is almost always demonstrated as a win over the long-running standard, so people run with the premise that the demo image of APCA is more contrast, rather than "ours say you'll have enough contrast to be accessible with a white foreground, even if it also says the contrast would be higher with a black foreground".
(source: in 2020 built color system around the same science, enabling latest iterations of Material theming)
refulgentis · 52m ago
Voters, I'd be very happy for feedback, I'm quite surprised it is -3.
troupo · 25m ago
I didn't vote, but "your article is wrong" take ignores literally the entire article, and the rather detailed explanation on why "bigger contrast by pure numbers is more contrast" does not work.
> in 2020 built color system around the same science, enabling latest iterations of Material theming
No wonder everything Google builds, including Material, always has issues with contrast.
https://youtu.be/tUJvE4xfTgo?si=vFlegFA_7lzijfSR (warning: video is in Portuguese)
Cant someone take a look at the buttons before the large project ships? Alternatively make it mandatory to never have black text on a dark button and tell every team member including the large ones.
Interesting to read about the perceptual contrast vs mathematical - I did not know that. Going to integrate that into my workflow.
> APCA says you don't need as much contrast
You can always specify the threshold if you want, e.g. "apcaContrast(color)) >= $targetContrast" after adjusting, depending on what you want to do.
It really is easy, just make sure you have enough color space.
re: just change APCA contrast target, that's separate from the Not Even Wrong stuff in the article. I didn't mean to imply APCA is wrong to say you need less contrast, but rather, that the article is wrong to conclude white has more contrast.
You are right, 0.18 is indeed perceptually closer to "middle gray" because the eye responds more sensitively to darker tones, so yeah, using a threshold closer to 0.18 makes more sense if we want to identify whether a color "feels" light or dark.
That said, 0.5 is a mathematical midpoint, but as I said, not aligned with how humans perceive brightness.
Ultimately one could use 0.18-0.3 as threshold.
The article says the standard specifies the calculation to use.
Consistent, it is not. Ex. we can imagine a background at L* 50 that is ~equally served with a white or black foreground - in that case, the aesthetic principles come into play.
To also disambiguate that, and get to 100% reliable, if both a darker and lighter color are available given contrast K and background color C, look at C, if it's L* is >= 60, choose lighter.
Then, it is 100% correct and consistent.
"Color Wheel: The Basic Color Theory for Artists and Designers" https://dessign.net/color-wheel-theory/
> Support for this feature first shipped in March 2021, in Safari Technology Preview 122.
https://webkit.org/blog/11577/release-notes-for-safari-techn...
> Added experimental support for CSS Color 5 color-contrast()
https://trac.webkit.org/changeset/273683/webkit/
- Their work does ensure contrast.
- The white on blue clearly has less contrast, not more. (squinting is a cheap way to test, or, walking backwards from your monitor)
With APCA, backgrounds around L* 60 tend to still allow white foregrounds, which is aesthetically closer to what the eye wants.
A black foreground would have more contrast regardless, even by APCA.
To be fair, this is how APCA is almost always demonstrated as a win over the long-running standard, so people run with the premise that the demo image of APCA is more contrast, rather than "ours say you'll have enough contrast to be accessible with a white foreground, even if it also says the contrast would be higher with a black foreground".
(source: in 2020 built color system around the same science, enabling latest iterations of Material theming)
> in 2020 built color system around the same science, enabling latest iterations of Material theming
No wonder everything Google builds, including Material, always has issues with contrast.