Intent to Ship: Relative Alpha Colors (CSS Color 5 alpha() function)

[Chromestatus]

Contact emails

cg...@chromium.org

Specification

https://drafts.csswg.org/css-color-5/#relative-alpha

Summary

Relative alpha colors refer to an origin color, and only change the alpha channel. The meaning of alpha channels is defined in CSS Color 4 § 4.2 Representing Transparency in Colors: the <alpha-value> syntax.

Blink component

Blink>CSS

Web Feature ID

Missing feature

Motivation

Relative alpha colors provide a direct CSS way to derive a translucent version of an existing color without rewriting its color channels. Authors currently need to duplicate component values or create separate precomputed tokens when they want “the same color, different opacity.” The CSS Color 5 alpha() function preserves the original color components and only changes alpha, which reduces authoring overhead and makes color tokens easier to reuse and maintain.

Initial public proposal

No information provided

TAG review

No information provided

TAG review status

Not applicable

Goals for experimentation

None

Risks

Interoperability and Compatibility

No information provided

Gecko: No signal (https://github.com/mozilla/standards-positions/issues/1396)

WebKit: No signal (https://github.com/WebKit/standards-positions/issues/657)

Web developers: No signals

Other signals:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

No information provided

Debuggability

No information provided

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

Yes

Is this feature fully tested by web-platform-tests?

Yes

Flag name on about://flags

No information provided

Finch feature name

CSSAlphaColorFunction

Rollout plan

Will ship enabled for all users

Requires code in //chrome?

False

Tracking bug

https://issues.chromium.org/issues/492246715

Estimated milestones

Shipping on desktop	150
Shipping on Android	150
Shipping on WebView	150

Anticipated spec changes

Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (e.g. links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (e.g., changing to naming or structure of the API in a non-backward-compatible way).

No information provided

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5070160203481088?gate=6508530389614592

Links to previous Intent discussions

Intent to Prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/69b4e4d0.050a0220.b9121.0139.GAE%40google.com

This intent message was generated by Chrome Platform Status.

[Alex Russell]

This seems extremely cool; is there perhaps an Explainer somewhere? This note on the Mozilla standards position request has most of that content and might help folks get more comfortable with the proposal as a stand-alone document;

https://github.com/mozilla/standards-positions/issues/1396#issuecomment-4363280736

Best,

Alex

[Vladimir Levin]

LGTM1

Thanks

[Chris Harrelson]

LGTM2

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[一丝]

Thanks for reviewing this. Let me write one.

[Rick Byers]

Thanks for proposing a new feature ID to track support for this feature, but it looks like the report was missing some information and so got closed. Ensuring we have a good summary description and tracking of features is really important to enable web developers and AI coding agents to reason about the availability of the feature (eg. see webstatus.dev and the baseline project). Please add the requested information to the feature ID request and reopen it (or file a new one).

Rick

--

[Yoav Weiss (@Shopify)]

https://nerdy.dev/relative-alpha seems like a signal.

 

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