Brief Answer: You should see a gastroenterologist. Detailed Answer: Hello, Thank you for using HCM. The black color of the stool is not related to appendix surgery. If everything went well during the surgery , the amount of blood lost within the bowels is to small to color the hole stool, and it does not last for days. It would have been helpful for me if you had written about any other symptoms either than black stool , such as stomach pain, malaise ect. Nevertheless i suggest you to be visited by a gastroenterologist and do a laboratory exam of the feces to see if it is blood within the sample or not. If it comes out to be negative, then it may be related to diet. There are some food that may cause black stool also, such as green vegetables, red beet, iron rich foods (such as cooked spleen), junk food etc. Be aware that the therapy with oral iron can cause black stools too. If it comes out to be positive for blood then you should undergo a fibrogastroscopy. Hope this is helpful. Let me know if you need more clarifications. Otherwise please close and rate the answer. Kind Regards, Dr. Juarda