LionelTin,
You are absolutely correct, for this exact reason I used a Black Rust-Oleum under coat when restoring our last 817 Caboose. Then I painted several coats of final High Gloss Black over it, to give the Black and Gold 817 the black color I actually wanted to achieve, at final out come.
Using the same color under coating, if you can find it, really does help achieve final color out come.
PCRR/Dave