css-color-4 introduces the concept of a host-syntax for color interpolation. For legacy colors, interpolation happens in sRGB for back compat reasons. When the relevant specs do not specify their own host-syntax for interpolation spaces, it falls back to OKLab for non-legacy colors.

We probably want to introduce a host-syntax for transitions and animations for explicitly specifying an interpolation space, and possibly also specify if the default interpolation space depends on which color space the endpoints or keyframe values are specified in.

See also issue #7567.

@mysteryDate