[csswg-drafts] [css-color-4] Clarify that `none` is allowed in calculations (#13752)

cdoublev has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-color-4] Clarify that `none` is allowed in calculations ==
Discussions and resolutions in #10151, #10211, #10280, suggest that `none` is allowed in calculations in color functions, with examples explicitly using `none` inside a math function, which seems unspecified, as opposed to RCS component keywords (emphasize added):

  > If an origin color is specified, the remaining arguments can either be specified directly, as normal, or be specified as a component keyword referring to one of the components of the origin color converted to the color space of the relative color. **Math functions can also use these keywords to do dynamic modifications of the origin color’s components.**

  > Within a relative color syntax `rgb()` or `rgba()` function, **the allowed component keywords are**:
  >
  > - `r`, `g`, and `b` [...]
  > - `alpha` [...]

This does not seem to be backed by any test on WPT, or supported in current versions of Chrome and FF (ESR).

Of course, if a relative color uses a math function containing a component keyword representing a channel value of the origin color that is specified with `none`, resolving the math function will require resolving `none`. But this does not imply allowing it in calculations, as long as it does not show up in the serialization of the resolved color value (the declared color value preserves the specified component keywords).

And I do not see how allowing it can be useful to authors.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/13752 using your GitHub account


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Received on Wednesday, 1 April 2026 06:20:06 UTC