These last 2 guy are right on. I was a painter a custom shop for years that used the PPG DAU and DBC paint system. Temperature is a huge factor in spraying metallics. You need to make sure you are using the right temp reducers and hardeners for starters. Secondly, make sure you have enough flash time inbetween coats - haste makes waste when it comes to painting. If you don't have enough flash time inbetween coats you will end up with the "modeling" effect you described earlier. Its basically the metallics in the paint running together (the dark spots). Overall, spraying with single stage metallics is difficult and is hard to get a nice finished product unless your familiar with them. In fact, we rarely used them in the shop because they are so unforgiving - if you make a mistake you can't wetsand and buff it out. Your best bet for a quality finish would be to use a basecoat/clearcoat system and add flattening agent to it, if you are looking for a semi-gloss appearence. However, take your time, add some distance from your spray gun to the metal and make sure you have enough flash time inbetween coats and it should turn out just fine.
Jeff
