It looks good and the manufacturer doesn't have to track blue wheels to fit on blue cars etc. He just needs four wheels for each new car of any colour. Same goes for stocks of spares. Remember when Henry Ford started mass production of cars with the Model T, he decreed it could be made in any colour as long as it was black, thus eliminating innumerable production glitches.
Thanks, ewood27. But the same could be said of colour coded bumpers, mirrors etc. I'm just curious about why silver? I wonder if it really looks best, or we have just become conditioned to that as the norm.