Hud - what he meant was colors like polished aluminum, chrome and such... if you are using regular aluminum then a well cured (48 hours to be safe) coat of Future actually has worked better for me than the black gloss enamel. Just spray a couple of thin coats then hit it with a couple of thicker coats (not too thick) until slightly glossy to glossy... let it dry for 48 hours and go to town on it!!! Use several light coats of Alclad in the beginning because too heavy of a Alclad coat could melt deeper than the future...
check out: http://www.alclad2.com/alclad-home.html and they list several other primers for the non-shiny finishes...