Pics aren't easy to find, but I've got a few of the bottom side of the '63-'82 interiors. From what I've been able to determine, they're made out of some kind of reinforced fiberglass, and the survivor series & Bloomington Gold experts from the Corvette forum I belong to (corvetteforum.com) all say they left the factory unpainted. Here are a few of the best examples I could find from a correctly restored '67:
Here's a pic of a red 1980 (maybe mine?) on the assembly line. As you can see, the fiberglass flooring etc is not painted. http://corvettec3.ca...a/images/20.jpg
I'm not just talking about finding an appropriate shade of paint, although I wouldn't mind recommendations. It's equally important to capture that raw fiberglass look as well.
* Tip of the hat to Custom Mike for the link to the pics.