I've got a couple extra grills and was looking at them yesterday. I've got one that looks like it was gray and had been painted black at some time. The black is starting to flake off, exposing the gray plastic. The other extra one I have is pretty rough. Its got multiple gouges out of it. That one looks to be black all the way through.
Maybe the Rallye grills weren't painted at all. THey were just molded in black plastic and left that way.
The lower valence piece was painted. It's molded in a tan plastic and was left bare on the under side.
If no one has any other suggestings, I'm going to try the SEM paint and see how it comes out.
Darren