MUTTSJET,
Wheels on #596 had gold paint on the spokes. I wish I knew the answers to your question about the finish on the prototype wheels. I'd like to spend the rest of the afternoon researching that but of course, life has other plans.
A cool trick is to finish with a clear coat but use what's called a 'knockdown' clear coat. Keeps things from looking too shiny. I think we used a 25% knockdown.
It gives a special glow to the wheels that's hard to describe. Pleasing to the eye but not distract from the rest of the car.