Groovy! Something to set them apart visually will help greatly.
By the way the poster before has a point that the confusion on the Republican side should be greater. They often didn't know which regiments where at what strength or if they were going to fight. Perhaps in the long term it should be considered if proper Army Command and command points doesn't give them an unfair advantage. At least in my current game, the Nationalist AI didn't pose any challenge from turn 1. The anarchist force in Catalunya was already enough to win a victory at Zaragoza, as well as capture lots of artillery. From there it has been a constant retreat for the Nationalists. The time the International Brigades have been kept as a reserve with the best artillery and all, and not even seen combat yet.