I don't have pictures of them, but I have 2 Leica M4-P's, both older brass top models, but one has worn down to the brass in places (looks like gold to me!), whilst the other has worn down less, such that the finish looks a bit lighter in tone, but still black. I guess that there is some coating of someting over the brass to help the dark colour stick better.
Sorry, it's obvious that i know nothing about metalurgy.