This is very, very simple idea (by simple, I mean that the idea itself is simple, not implementation - i lack of knowlege to put such assumption). When starting invasion campaing, let us choose if we want to play as green, grey or brown. With faction specific weapons it does make sense now to prefer one side, over other two. Also just having diffrent color than all the time green would be nice from time to time.

Yup, that is coming.