Hey Spong
Thanks for that info--very interesting. Check out T. Mails's Mystic Warriors of the Plains for some other useful info on plains warpaint, including painting horses.
It's funny cause I think there's a mix of individual creative license and long-standing symbolic tradition. For instance, there was a very systematic regulation amongst some of the plains Indians for how to wear/mark feathers for achievements. I doubt that much allowance would be made for freedom in that regard as they were as anal as WWI German pilots counting kills when it came to counting coups. I think some of the warpaint was also dictated by symbolic tradition even thought there was quite a bit of commerce in symbols amongst the tribes.
I think the stickling point here is that if a warrior wanted to get funky and make up his own face/body paint to look cool/terrifying he had full license, but if he wanted to use marks that indicated achievements--how many horses stolen, wounds received, etc. he had to follow strict conventions--otherwise he'd be screwing up social norms.
Obviously color has a lot of mythic and/or symbolic meaning for Native American cultures and using a color in a totally inappropriate context--say green to symbolize a successful revenge raid rather than the traditional black would just not make senese to anyone so the warrior would stick to the black. In a way we're talking about a symbolic language here where the freestyle painting is akin to poetry and the codified colors/symbols akin to social contracts.
AX