[css-color-4] Effect of working color space on computed & used values

[svgeesus]

Originally reported by @svgeesus as an inline issue

Define if changing the working color space should have any impact on the above.

[svgeesus]

Tidying up this old issue. As stated in Resolving <color> values, Computed and used values should remain as specified, modulo decisions about unitary alpha (and commas, for the sRGB ones) so working color space does not affect them. It will affect interpolation, and other places where calculation is done on colors.