Your last comment confused me. Go over it with DP48 and then go over it again?
I didn't know the DP40s were still available, those are the ones with chrome in them aren't they?
I did, DP90 black over bare metal, K36 high solids primer, block sand, DP90 black, and then dark metallic blue. I put the second layer of DP90 on to give the blue a darker appearance.
Don't think it's really necessary unless you're worried about adhesion between different layers of paint or unless you want a single color under your top color coat.
Owen