Yes it turns dark with time if you don't remove patina from the case. Your picture is an extreme example. Normally people hasten the process with egg yolk or salty water etc just to give it a beaten older look.
By: Pun : December 18th, 2019-08:53
I’ve a Carl Braesher LE diver watch. It’s two years old and has developed light patina. Bronze is hard and tougher metal as compared to steel or gold, so keep its sharp edges away from other softer metal watches or laptops etc. I like it’s ruggedness. It ages very well indeed.