Old friend of mine used to use different base colors that helped them differentiate character type at a glance.
For example, all the aloof characters were variations on an ice blue base, all the deviant and super horny characters were based upon hooker red, and so on. Also characters that were enemies, rivals, or full on nemeses were at opposing sides of the color wheel.
Probably more complicated than you want to make it, just thought it might be something interesting that could help with your brainstorming.