Green tracers may not be as silly as they seem. I've read an article somewhere before that said that the Russians did indeed use green tracers in their ammunition. When I saw the AKs shooting green in OFP I thought it was pretty nifty.
Oh wait, here's a cool wiki article on the subject.
Apparently the green light is produced by barium salts.
http://en.wikipedia.org/wiki/Tracer_ammunition