I just realized that when we speak of metallics, we could mean either of two different things:
1) Paint that's supposed to result in the part looking like it's made out of a type of metal in its "natural" state - e.g. aluminum, steel, chrome, etc...
2) metallic flake paint like one gets from a typical (real) automotive paint (e.g. "dark metallic blue")
The type of paint that works for 1) is not at all what is needed for 2). I feel a bit silly, but it just now dawned on me that I need to think about what is being discussed!