This is a picture from a colonoscopy and the person was diagnosed as having Ulcerative Colitis, when they actually had Blastocystis Hominis parasites. Compare with the picture below from Wikipedia. There are a lot of similarities. A colonoscopy can show the ulcerations but it will not tell you the cause of your UC symptoms.
“Endoscopic image of a sigmoid colon afflicted with ulcerative colitis. Note the vascular pattern of the colon granularity and focal friability of the mucosa.”