Re: [csswg-drafts] [css-color-adjust-1] Is forced background-color computed or used value? (#4915)

The CSS Working Group just discussed `Is forced background-color computed or used value?`, and agreed to the following:

* `RESOLVED: The color computed values are defined as used values using the color mix function`

<details><summary>The full IRC log of that discussion</summary>
&lt;dael> Topic: Is forced background-color computed or used value?<br>
&lt;dael> github: https://github.com/w3c/csswg-drafts/issues/4915<br>
&lt;dael> Rossen_: This is in the context of forced-colors-adjust.<br>
&lt;dael> Rossen_: Short summary is in the previous impl of what used to be ms-high-contrast and is now forced-colors we were reverting colors incl background and override with system color<br>
&lt;dael> Rossen_: At the time at MS we didn't consider taking in the alpha channel of the color value.<br>
&lt;dael> Rossen_: That meant simply all overrides were stable during computed and alpha was always opauqe<br>
&lt;dael> Rossen_: When working on focred-colors one addition to the feature is addition of considering alpha channel of the color. For background-color it means we now have to compute the final color value during used time<br>
&lt;dael> Rossen_: That's how issue came about. Is it supposed to be computed or used.<br>
&lt;dael> Rossen_: Is amelia_br or fantasai on?<br>
&lt;dael> TabAtkins: We have me and I commented<br>
&lt;dael> TabAtkins: Seems clear this needs to be used value time transformation<br>
&lt;dael> TabAtkins: because we can't do anything with a system color until we resolve it which is at used value time b/c need to know color scheme<br>
&lt;dael> TabAtkins: This is to make it reasonably work. Amelia's comment brings up the very good point that color mix function would be useful for this.<br>
&lt;dael> TabAtkins: If you want to define a computed value that's this system color but with the other alpha you can do it simply with color mix function.<br>
&lt;dael> TabAtkins: We could and should define computed value of color becomes a color mix function with alpha from previous color and mix with system color<br>
&lt;dael> Rossen_: What do we serialize in OM? used value?<br>
&lt;dael> TabAtkins: All current properties do used<br>
&lt;dael> Rossen_: Okay, that continues to work<br>
&lt;dael> TabAtkins: Not 100% clear/remember what happens in image properties. But plain colors do used value.<br>
&lt;dael> Rossen_: The ones covered by color-adjust are covered.<br>
&lt;dael> TabAtkins: Yeah<br>
&lt;dael> emilio: Not quite used value because :visited and so on<br>
&lt;dael> Rossen_: sure<br>
&lt;dael> TabAtkins: Ignoring :visited hacks they are always used values<br>
&lt;dael> Rossen_: Sounds like a good path forward for this behavior<br>
&lt;dael> Rossen_: Any other considerations or proposals to consider?<br>
&lt;dael> TabAtkins: If we go with this is means impl should prioritize color mix.<br>
&lt;dael> TabAtkins: Also solves that you can't transition system colors since you can use color mix for that.<br>
&lt;dael> Rossen_: Sounds good<br>
&lt;dael> Rossen_: Looking for your summary<br>
&lt;TabAtkins> color-mix(appropriate-system-color, specified-color a(100%))<br>
&lt;dael> Rossen_: Prop: The color computed values are defined as used values using the color mix function<br>
&lt;dael> Rossen_: Objections?<br>
&lt;dael> RESOLVED: The color computed values are defined as used values using the color mix function<br>
</details>


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Received on Wednesday, 20 May 2020 16:12:01 UTC