[css-color] Serializing color() values

[grorg]

How should values defined using color() be serialized in computed style?

1. Should color(a b c) or color(srgb a b c) values be output as rgb()?
2. Should color(someprofile a b c) values that end up inside sRGB be output as rgb()?

[SebastianZ]

I tend to agree with Tab's statement to treat rgb()/rgba() as legacy syntax. Therefore I think it should compute to color(a b c) and color(a b c / d) in those cases.

Sebastian

[svgeesus]

I agree with Tab and SebastianZ

[grorg]

Treating it as legacy syntax is fine for input. But the output from computed style is probably parsed by a lot of content on the Web. If that all of a sudden changes to something unexpected, the world will collapse, the seas will rise, and Trump may get elected.

[upsuper]

Agree with @grorg, unless someone can prove that changing this output is web-compatible.

[grorg]

Wow. I'm regretting my last statement now.

[cabanier]

:-(
It's all your fault!

[frivoal]

Reposting a comment I made in #742 as I am closing that one as duplicate:

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The css-color-4 definition of the computed value of the color property says :

Computed value: an RGBA color

That doesn't sound right:

• This is not entirely clear what is meant by that. The simplest interpretation is that the value should be computed to the rgba() function, but maybe something else is intended.
• If computing to rgba() is intended, this appears to contradicts css-color-3. The rule there is phrased in a somewhat ambiguous way, but seems to imply that basic colors, hex colors, and rgb() colors should be computed to the six digit hex value or rgb() functional value, while other notations should be preserved as specified.
• Browsers today (checked Chrome, Firefox, Safari, Edge, Presto) interoperably return rgb() (not rgba()) as the computed value of hex colors or named colors when exposing it through getComputedStyle. In contradiction of css-color-3, All also do so for hsl() colors. And but all but Edge also for rgba() and hsla() colors with an alpha of 1 (Edge compute both to rgba()).
• How to convert color() colors to rgba() is non trivial and lossy. It needs to happen eventually to be able to paint, but computed value time seems wrong.

If the level 4 text is meant to be different from the level 3, we should errata level 3, and be clearer about what exactly is meant. But given the compat data and the newer color functions, neither "always rgba()" nor “as specified, except but #rrggbb rgb() and named colors” seems to be the right answer. I think we should specify what is already inter-operable (and see if Edge is willing to join everyone else on computing rgba(*,*,*,1) and hsla(*,*,*,1) to rgb().

The new color functions that do not yet have a compat baggage, so we should probably be clear before they get one. We could keep them as specified, or maybe convert them to a base notation: gray()and lch() -> lab(), hwb() and hwb()-> color(), omit the alpha component when it is 1.

As for the comma-less version of rgb() and hsl(), we also should decide if the compute to the legacy syntax (with commas), preseve them as written, or compute to color()...