How does the 'race' system work for GTA IV peds?

I'm specifically referring to the little _whi/_chi/_bla thing at the end of some textures. I tried working a mod with a series of extra head and short sleeve textures for m_y_cop, but only _bla and _lat (and _uni, but that means "universal" so it doesn't matter) seemed to be recognized as a shirt color, and only _whi _chi _ara _bla and _lat are acceptable as head textures. By acceptable, I mean the game will spawn with them. So like, is there a .dat file or something that controls how many races have been assigned to a particular pedestrian?