Honestly, it gets pretty dark. I prefer a contrast, of dark and light. If you are sold on the black exterior, I would get the gray interior, it looks very nice, especially with the 2-tone dash. If you are sold on the black interior, then I would go lighter (silver) on the exterior which is easier to keep clean. I would also consider where you live, black gets pretty hot. I am in Minnesota, so it isn't as much of a factor, but I know keeping black clean is a pain in the ass!
Best of luck with your decision...