From what I understood from a bender once and had the same thing. I think they called it "Rapid Transit". Meaning the food is moving too fast through your digestive track. Not a good sign. See a doctor. Mine went away after a few days of NOT drinking and eating good foods. Just my 2 cents.
Also too much sugar in your diet could be responsible. I wouldn't be concerned unless it continues as mentioned above.
It really depends on how long you've been drinking.. Me personally, i haven't experienced any green stool (little shakes and sweats) but i would drink lots of liquids (gatorade is amazing) and if it doesn't get better in 24-48 hours i would see a doctor. I could be serious if left untreated...
Alcohol withdrawal is very serious and can be fatal. But in answer to your question: your stool may contain bile, which is greenish.You should see a physician ASAP. Especially if you are having shakes or tremors; these are not good signs. Good luck and God bless.