Maybe the trick is as many armies before have used is the idea of a tabard or other decorative piece worn over the armor to identify what faction or in this case tribe you belong to. Until (or if) such a system come into play the previously mentioned specific armor/colored pieces could work for each tribe to ID themselves
Not a bad idea Blake IMO. I would love to be able to change the color of armor as in dye it. That would be cool and solve the issue. (come on Bow weapons!!)