Feature request: Statically tagged color struct

Nobody has claimed this yet.

I have a particular use case which requires a large array of colors that can be converted in-place between `AlphaColor`, `OpaqueColor`, and `PremulColor`. This array is homogeneous and the shared element type is known at compile time. Using `DynamicColor` is not a good solution, since it not only adds an overhead of 4 bytes per color (discriminants are padded to align to `f32`), but also ruins the oblivious cache line alignment that `[f32; 4]` provides, going from 16 to 20 bytes per color.

For this reason, I think it would be useful to have a statically tagged color type (`Color`) that internally contains an `[f32; 4]` and assumes a fixed alpha value of `1.0` for the opaque case. This change would not only allow in-place conversion between all the statically-sized color structs, but would also guarantee cache line alignment which would be helpful both for performance and for multi-threaded operations. The only drawback would be that storing opaque colors would waste 4 bytes per color.

Any thoughts on this?

Start by reviewing the existing AlphaColor, OpaqueColor, PremulColor, DynamicColor, ColorSpace, and ColorKind concepts mentioned in the request. Clarify the proposed API, conversion behavior, storage guarantees, and acceptance criteria before implementation; the issue does not currently define a concrete done state.

Written by the indexing model from the issue text.