Rectal bleeding commonly occurs following a bowel movement and reveals itself by showing up as bright red blood on the toilet paper. It is the color of blood that indicates how serious the problem is. When the blood is bright red it usually indicates that the bleeding is low in the colon or within the rectum. This type of bleeding is usually not serious. The darker the blood, the more serious the problem may be. However, not all rectal bleeding is seen by the eye.