I think the trick to be instead of faction specific what color combines would fit to the faction. Right now there are two we have the standard red and green and there was a tournament prize orange and grey.

With those 2 we have a total of 4 different color combination. But we have 7 factions. Adding one more color attack/defense die would give us 6. Adding one more color attack and one more color defense would give us 9 different combinations. Adding two more color attack (or defense) dice would give us 8 different combinations.

So now the only question is what colors would they be and which faction would use which combination. (I.e. Resistance is Red and Grey).