Originally Posted by
big chainring
Why do you want a clean chain? Oil in whatever form is a good thing.
All things considered, I cannot see any advantage to a layer of dirt or metal shavings on a bike chain but there are several to a clean but lubricated chain. As for black, well, some of my bikes have KMC chains which are black to begin with but not from dirt. My old Schwinn with the 3speed SA hubs has a chainguard and I don't care how wet the the lube is on it really, but I still wipe it down when I see it is collecting smegma from the road.