I\'ve been priming white for a while and adding a \"guide coat\" wash to darken the deep places.
Sometimes though you can prime one color and selectively undercoat with another. Last night I had a chance to sit down with Tim Lison for a while (oh, you name dropper!) and he showed me why my metallics suck so bad. My white priming was a big part of the problem, and he suggested undercoating very dark in the parts that were going to get metallics after priming.