Metallic black with a lot of gloss. Nice and simple, and if a McLaren could be understated, this would be it.
I do like the following colors as well:
Candy apple red with black interior.
Navy blue with tan/brown interior.
Orange.
All on HDF cars where the black wheels and spoiler and front lip set off the colors nicely. On the blue car, I would have the polished silver wheels, though. I think they are called a satin finish. I definitely wouldn't ever put chrome on a McLaren.