Why is my poop green?

I can only guess. I guess you have eaten canned spinach.

A lot of fat will make your poop yellow. Internal bleeding will make it red or black like coffee grounds, depending on where the bleeding is. Cocoa pudding will make it super dark brown. Red, yellow, or green peppers (skins) can go through without being digested, making red, yellow, or green specs in your poop.

You need fiber to hold your poop together and clean the pipes. Wheat bran is the best kind. Two slices of whole grain bread every day is a minimum, or veggies with every meal.