I have found that some acidic solvents (used), for removing calcium lime rust (CLR), tend to deposit a pinkish copper film layer on steel parts; the acid is not exposing any existing copper alloy content.
And then there is the red and yellow brasses and bronzes, and the leaded and unleaded.
A benefit of brass ball bearings on a show bike might be that they would not be a source of rust. I avoid bronze hardware on bicycles, including axle or stem washers, but use them (painted or not), sometimes even with nylon washers, for fender mounting hardware.