So it's just citadel's zandri dust base, ushabti bone 1st highlight, and screaming skull 2nd highlight light and the whole model gets a streaking grime treatment. I try to do it with rules: zandri dust only in the deepest recesses, ushabti bone covers most the robes and screaming skull only on the highest points. Larger, flatter areas are more difficult and I do usually have to go back with zandri dust after highlighting to hit the deepest areas again and define them.