I've found white, cream and even gold in multiple places on the quarter panels. I've wandered if the fender tag has been replaced but I dont know. The door panel metal is painted black where it is usually body color and I have seen what appears to be black over spray in a few hidden corners.
But i agree that it sounds unlikely. I don't see any hard proof of a vinyl top either. However if somebody dedicated enough got rid of the top, did it right, they may have painted it correctly.
The puzzles of the old cars.