I emailed my GI and he called me right back saying that dark colouring in Chinese food can cause dark stools especially if the colouring is liquid.
He said he wasn't worried at all and for me to monitor it over a few days.
I have IBS and today I also got diarrhea but the stool colour remained a very dark brown/black colour. Surely the blood would would show on the toilet tissue and stools if they have come through my tract so fast as to give me D?
I hope I am worrying over nothing.