Different designs demand different colours. There are a multitude of characters that can ever only look good with the colour that they've been designed with. As such, colour alone is a poor criteria to pick characters with.
However, I digress. I have found that the usual trend in my favourite characters tend to have green hair. ( Asa, C.C., Vanilla H, Lyndis, Chachamaru, Motoko (it's black- but it's usually depicted with green highlights), Nephenee, LOL Fang-tan (or Tsuruya, if you prefer), etc. ad nauseum).