The Cause of Penile Discoloration/Darkening

again, from the Net….

“…penile trauma can create pinpoint bruising, called petechae, in which blood is drawn through the cell walls into surrounding areas, where it is later reabsorbed. The iron in this blood then oxidizes, creating a dark brown tint (wet rust). Over time, the entire penis becomes very dark….”

Probably hemosiderin deposits. See this post and the whole thread in general.