I haven't seen a color that I didn't like on the XF.
I like white the best, it looks so clean. The metallic colors DO reflect the light better, but I live in Michigan and the sun doesn't seem to shine that much anyway! I have the 2-tone grey interior, and I love it. The Cedar is too harsh for my taste, but that's just my taste.
What color are you looking at for the ext? It has to be something that you are completely down with, or it'll give you an attitude about the car that will stay with you. I guess that's why you started this thread. You need to validate your choice so you're not sorry afterwards. Around here, I see black out numbers any color in the coupe. If I was getting a coupe, I'd get anything but black for that reason. Too many others are black.
Good luck!