Instead of one plain simple colour I was thinkin that maybe hair could have about 2-4 sections of which can be coloured differently. This could work for rainbow sets. I was thinking for this to be mainly for Mohawk/Minihawk/Centurian. So the front bit can be blue, middle can be yellow, back can be purple. That's just some random colours but that's the simple layout for it. Front, Middle, Back. It's pretty much just hair color but your hair can have more than one colour, so a colour mix in a way. These color sections can be sold for different hairstyles and the owner can choose which hair colours they want in it. It's not something important but it would look pretty nice with sets.

Maybe a special section for ''Hair colours'',you buy each hair colour,then you can place it around in that section,according to your hair.