Melanosis coli, also pseudomelanosis coli, is a disorder of pigmentation of the wall of the colon, often identified at the time of colonoscopy. It is benign, and may have no significant correlation with disease. The brown pigment is lipofuscin in macrophages, not melanin.
Read more about Melanosis Coli: Etiology, Histologic Appearance, Prognosis, Relation To True Melanoses, Non-colonic Pseudomelanoses, Additional Images