I just have been having this problem for 2 weeks. I have had vertigo nausea and throwing up. Now orange-red stools that were so dark they looked like blood. I have not ate anything of darker nature like beets etc that can cause change. I read something about bowel salts at one point out of curiosity maybe if there isn't enough it causes change in bowel color. I went to the lab today to do cbc,. stool and c-diff testing hopefully we can help one another by finding out the reason. I have been feeling bad and don't really feel that great. Cramping stomach wise and bathroom from diarrhea to watery stool....
I'd go to your doctor and ask. It could be from something in your diet.
I also forgot to mention that these symptoms started occuring the day after my period ended. I don't know if this is of any revelance though...