First of all Congratulations to your decision of buying a Cayenne! It's really difficult to choose between those two colours! I saw a blue Cayenne Turbo some time ago and I have really to say, that it looked great. Normally every Cayenne is black or silver, but a blue one is extremely rare - at least at our streets here in germany.
So I would personally go for a blue Cayenne - but I wouldn't know for which interior colour I should decide myself. It's extremely difficult, in my opinion, to find a perfect colour for the interior, when it is a blue car...

edit: photo of blue Cayenne (pre-facelift model, but the colour is great )