I had the same issues for a 67 Corvette. Red plastics under a planned silver paint. Base voted with tan filler. Then the silver by revell with my airbrush. After the clear cote (2K) the red came slightly through. It looked a little pinkish.
I took the paint of and started again. The same procedure. A friend of mine gave me the Tipp, to put only really thin layers of clear cote on it. Up to four times. Not that much that you'll get a smooth surface.
I did that. After three "foggy" layers and letting them dry, I put a final layer of clear coat on it. That helped.
I pictured that in my wip: 1967 Corvette Coupe C2 | Project by christian-w (1:25)
Another try could be: base coat in black, than silver over it and after that the color you want. That could help.
29. September, 16:55