The only thing I could probably wish for is being able to modify the name of the color a little. Instead of 'black' being able to change it to 'oily black' or 'dirty black' or things like that, and have the block show up in the regular color it would. As it is, you can write something like '%S is wearing a oily $color shirt', but then only the $color part is colored, and I feel like the high lights offer some good data into the truly distinguished color of the garment at a glance.
But as far as visible colors on the spectrum go, I think we have more than enough color already.
It'd need to come from one source because you'll need to allow it to change from dyeing for the %color modifier.
I don't know how much work it would take. Also I support implementation of more pinks into the color files! There's already a custom displayed pink color in the game. Let pink break free! Who cares if it's probably technically just a renamed fuchsia!