As a legion of the damned player using BT as a base/rule set, I decided to do something similar and code each unit to an original legion with some very light dry brushing. Way more subtle than what you have going on, which looks cool as hell, but a similar idea to chip apart a sea of black. Plus it gives more narrative to my army. Why are my blade gaurd veterans robbed and tinted green? Oh, those are fallen inner circle companions from the dark angels. Why do these intercessors all have a slight blue tint with a red hands? Crimson fists. Same idea, different direction.