What about if it’s a mid-grey (Titanium) car then?!....
I don’t disagree with you, but there are so many examples of dark cars with dark wheels and vice-versa that I think its on a case by case basis.
With regards my mid-grey car, I'm only talking about having them done a few shades darker, so they wont be as dark as say the Nismo wheels but will be noticeably darker than the standard silvery finish. Much the same as after a couple of weeks of road grim and brake dust.