This may sound strange but i recently took my child to see a chiropractor and the chiro asked me if my child had been having greenish coloured poos, I replied that he had and he told me that his back was out right in the area that can have some effect on bowel movements, he corrected his back and the green colour has now gone. Just a thought or idea of something different to try. The back's nervous system controls alot of the body functions.
I just recently had a flight from the East Coast to the West Coast. At the airport I bought a blueberry bagle and when eating it on the plane I noticed the whole thing looked blue, even the breading part of the bagle. The next day I had heavy green stools that lasted for two days. After two days it went away so it was obvious that the bagel and the dyes had something to do with it. Hope that is similar to your case.