I am surprised on how many body colours that black wheels actually look good on. I thought they would look good mainly on black or white cars, but blue, red cars etc also set them off.
I have just recently removed my 21" BMW OEM Star Spokes and replaced them with 22" X6M reps. I was very close to painting them a gloss or even a matt black but I worried the car would look too "gangsta" and my wife, who mostly drives the X5, would not have been overly impressed. So I opted for a gunmetal grey. That said my X5 is Carbon Black and the black on black would have been too much. As your car body colour is grey I think you get away with it. Just!