I'm just finishing week two of driving my Carbon Black X3 and haven't washed it yet (don't worry...washing it today).
It's a bit dusty right now but still looks good. With the dust on it the dark blue is not coming through as much in the sunlight but it still shows. When it's clean it is incredible. Everyone commented on the colour asking me if it was blue or black.
I does show finger marks though when clean. My 8 year olds hand prints are all over the back door handle area. But that's just life I guess!