I like black and sealgrey. But I wouldn't go for black because you can see any tiny scratch, dust particle, etc....horrible.
I saw a yellow 997 and it looked weird. I also saw guards red which looks interesting and what might be a great color is slate grey, not available yet.
Forget about any green colours, they look horrible on the 997. I also don't like the met. blue (sorry, don't remember the colour name) 997 Carrera S at my dealer too much.