i believe originally the color was put into the molded plastic itself. at least that is how my original ones appear to be. i redid mine with the light silver argent.
man i'm foggy tonight you are right it was cast blk.. i had a old qt of ppg light argent that i used on mine. i did it so long ago i half forgot about it. got another one to do,maybe try the krylon, but i prefer to use my gun before a bomb.
I just restored a 71 Road Runner grille recently for a friend. My top secret paint for the surround and headlight openings is Eastwood's Spray Gray. No texture, very high solids for one coat and it's a dead nuts match to the original low mile one I recently sold. Here's some pics.