Stools sometimes are coloured that way due to bile and fast transit of food in your intestines.
I have had this a long time--over last couple of years, coupled with gas, food allergies and other symptoms. Sorry to be explicit, but for a long while they were loose, but now as I'm improving, they're more solid but still green.. I too have been wondering what that's all about!! I think I may have some sort of intestinal candida problem--it seems to be responding fairly well to nystatin--so maybe that's the cause??
I will consider it a little victory when my stools turn back to a more 'normal' colour!! (although apparently 'green' is considered 'normal' by conventional medicine)