I would test the metallic over the white krylon on a test panel. Auto paints tend to have strong solvents that melt most other paints. Primers tend to evaporate fast so they dont attack, but to get gloss the colors dry slower,eating what is under. I have had planes in all duplicolor but never mixed brands. also make a test for sanding; I have sanded real cars with metallic before clearing that looked like it should. Your just going to have to make a test panel.