Melanosis coli. Endoscopic view of the interior of a patient's colon affected by melanosis coli (pseudomelanosis coli). This benign condition causes brown pigmentation of the lining of the colon and is associated with the over use of laxatives, particularly anthracene type cathartics: cascara, senna, aloe, rhubarb and frangula. Cessation of the laxative results in disappearance of the pigmentation. Lymph follicles and polyps do not take up the pigment.