[css-color-4] Should premultiplied undefined alpha make other color components undefined?

[facelessuser]

Reading over the spec, it seems that if the alpha component is none, that all the associated color components will also become none. This seems unintuitive (at least to me). To me, it would seem that premultiplication should not be performed if alpha is none:

>>> Color('color(srgb 1 0 0 / 0.5)').mix('color(srgb 0 0 1 / none)', space='srgb')
color(srgb 0.5 0 0.5 / 0.5)
>>> Color('color(srgb 1 0 0 / 0.5)').mix('color(srgb 0 0 1 / none)', space='srgb', premultiplied=True)
color(srgb 1 0 0 / 0.5)

I guess, what I expected to happen was for it to behave as if premultiplied was disabled, because how can you premultiply if you don't know by what to premultiply? This would just take alpha out of the calculation.

>>> Color('color(srgb 1 0 0 / 0.5)').mix('color(srgb 0 0 1 / none)', space='srgb')
color(srgb 0.5 0 1 / 0.5)
>>> Color('color(srgb 1 0 0 / 0.5)').mix('color(srgb 0 0 1 / none)', space='srgb', premultiplied=True)
color(srgb 0.5 0 1 / 0.5)

There may be reasons for this, but I am curious if there is something driving this decision, or if maybe it just wasn't considered.

[svgeesus]

Alpha being none was forgotten about for premultiplication.

If any component value is none, the premultiplied value is also none.

That is referring to the color components only, not the alpha. However, we didn't forget for un-premultiplication, if alpha was 0:

If the alpha value is zero, the un-premultiplied value is the premultiplied value

So I propose to fix that, in premultiplication:

If the alpha value is none, the premultiplied value is the un-premultiplied value

and in un-premultiplication:

If the alpha value is zero or none, the un-premultiplied value is the premultiplied value

[facelessuser]

That sounds great to me!