[csswg-drafts] [css-color][css-animations] Is it specified anywhere that a color animation at time=0 exactly match the from color's computed value? (#13269)

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

== [css-color][css-animations] Is it specified anywhere that a color animation at time=0 exactly match the from color's computed value? ==
In the WPT test http://wpt.live/css/css-animations/animate-with-background-color-oklch-002.html, the first subtest is testing an animation from `background: #ff0000` to `background-color: oklch(45% 0.2 264)` at a few different time steps as described by this list:

```
  const bg_color_legacy_rgb_to_oklch = [
    { at: 0, value: 'rgb(255, 0, 0)' },
    { at: 0.25, value: 'oklab(0.583475 0.163433 0.0446685)' },
    { at: 0.5, value: 'oklab(0.538983 0.101987 -0.0365225)' },
    { at: 0.75, value: 'oklab(0.494492 0.0405407 -0.117713)' },
    { at: 1, value: 'oklab(0.45 -0.0209057 -0.198904)' }
  ];
```

Generally, when computing the value of a color animation at a particular time step, it is going to have a computed value that is serialized as OkLab color, since that is the interpolation color space. 

This test however, assumes that at time=0, the computed value should be precise value of the from color, which has a computed value using the legacy RGB serialization.

Is this behavior, of acting like no interpolation happed at all, specified anywhere?

(cc @birtles, @dbaron, @graouts, @svgeesus). 

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/13269 using your GitHub account


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Received on Thursday, 25 December 2025 18:14:30 UTC