Re: [csswg-drafts] [css-color-4] Clarify how to resolve `<system-color>` (#13719)

To elaborate on my previous comment (after a more in-depth research).

  > > To maintain legibility, the `<system-color>` keywords also respond to light mode or dark mode changes.
  >
  > This statement is not backed by any defined requirement.

This [comment](https://github.com/w3c/csswg-drafts/issues/6773#issuecomment-1098285102) confirms that this requirement needs to be defined (emphasize added):

  > There may be some updates needed around `color-scheme`, as well. (i.e. to **clarify that it affects the computed value of system colors**)

It was written before the resolution to use the corresponding `<system-color>` value in its colorspace as the computed value, instead of the specified keyword.

However, I would expect it to be clarified in [ยง 14.5. Resolving other colors (CSS Color)](https://drafts.csswg.org/css-color-4/#resolving-other-colors), which currently only says this:

  > The declared value for each `<system-color>` keyword and `<deprecated-color>` keyword is itself. The computed value is the corresponding color in its color space.

Similarly, I was not expecting to find the [`<system-color>` mappings](https://drafts.csswg.org/css-color-adjust-1/#forced-color-palettes) in CSS Color Adjustment, fwiw.

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[These comments](https://github.com/w3c/csswg-drafts/issues/3873#issuecomment-548001301) also suggest that how to compute `<deprecated-color>` is also currently underspecified:

  > Dropping a note here to say: don't forget to say how these values compute, if they compute to other keyword values or to a fixed color or to themselves. (I'm guessing fewer keywords that compute to themselves here is better for implementations.)

  > Given that these are legacy values for legacy compat & we don't want authors using them in new content, we can probably safely define them all as light mode values.

And #13459 asked if `<deprecated-color>`s should be (parse time) aliases of `<system-color>`s.

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  > But light mode or dark mode changes seems restrictive.

I thought other modes than light/dark modes exist tbh. But my point was also that the linked algorithm does not just consider the user preferred color scheme.

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Received on Thursday, 26 March 2026 07:47:46 UTC