It seems to be a glitch mostly with factory wheels. You can sometimes get around it with using the "two tone" paint option, and just setting both colors to the same color. I've got black factory wheels on several of my race cars using that method.
You can paint your cars proper black by using the "two tone" option in the special paints area, and setting both colors to 0/0/0.
Man I hope if we get a Shadow it's a Can Am car and not an F1 car. It would probably make the most sense to get the DN4, but I want this ridiculous looking deathtrap:
View attachment 1296647
Also the SARD MC8-R would be awesome.