Well, I'm a professional graphic artist/designer (make of that what you will...)
So in my "professional" opinion, don't go with tan. It's too similar in tone with gold and the car will wind up looking kind of "blah".
You want a color that contrasts with the exterior, but that also complements it.
I'd go with either red, black or white. Any of those colors would work great with the gold body. Or if you want to go a little "out of the box", how about a turquoise?