Since this mucosa is like in the pouch on one side, it is just normal, if the
stool is
black only on one
side. This would go with middle right abdominal pain (not necessary). There is not always so much mixing inside the bowel, as you might think.
Another: if you have inflammed diverticles (diverticulitis) in the last part of the colon, stool can be trapped there, inflammation can cause bleeding or not, anyway, some old stool can be dark.
What to do:
1. Is it blood or not (reliable lab test).