Guess I should clarify.... Not only the calipers but the silver disc behind the wheel also.
He means the center of the rotor where the wheel mounts up. I bought my car with 6200 miles on it from dealer. It was a service loaner from Pennsylvania. The rotor centers were fairly rusty from i'm guessing road salt. I used "rust eater" and then washed it off, used blow dryer to evaporate the water, then painted with brush using silver rustoleum. It looked 100% better without the rust and looked like fresh cast iron after painting. The sales guy suggested it. He had done the same to his 335i.