I read up on pepto and stool color and that's probably it. If it doesn't go away in a couple of days then it sounds like it could be blood, but I would expect blood to be more of a reddish black instead of a greenish black.
I've read your posts, and it sounds like we're having a similar experience with the flushes. I couldn't wait a whole 2 weeks between flushes either. It will be 2 weeks before my next flush and I hope that makes it more eventful. Good luck!