I'm assuming you mean like a Chaos IG
infiTRAITOR's Chaos Guard
is one of the best I've ever seen, and certainly a good place to draw inspiration.
Otherwise, renegades are usually a rag-tag group. Browns and khahis for equipment, black guns, some metal looking bits, and something more vivid for chaos icons and other parts where you want to draw the eye.
Maybe if you gave us some more info on your army we could help better.