Melanosis coli** Melanosis coli is a benign, reversible condition characterized by brown black pigmentation of the colonic mucosa, most often due to chronic use of anthraquinone laxatives. The discoloration is caused Mucosal melanocytic macules Mucosal melanocytic macules Black and Brown: Non neoplastic Pigmentation of the Oral Mucosa Head and Neck Pathology Springer Nature Link