I decided to go with a black badge as I also have every other trim piece gloss black.
A nice accent would be to have the surface gloss black and the side portion white (like
IND just recently did) http://flic.kr/p/dWCHHo
As for exhaust tips I went with black/CF tips , but if you'd plan to have a black / CF diffuser
silver tips would give you more contrast (I will have no choice and end up with CF tips and dark rear diffuser)
All comes down to personal preference (there's no right or wrong