Oh, slightly unrelated to colors but very much related to hairs -- there are a few old hairstyles that could probably be separated into different parts. Figure that'd be a lot of work, but it's worth a suggestion.
So, for example, here's the Spiked Pony Hair:

It would be nice if we could perhaps have that hairstyle without the eyebrows. Having that tail as a separate style would be nice, too, as you've already started to do with items like Patience/Patient hair.
Maybe Avril Hair could be separated into that top pulled-back part and the sides?