Yes, first figure out if you've eaten a lot of green veggies. If that's the case, you have nothing to worry about. The extra fiber is excellent for you. Also, if you started a medication for reflux, that can happen during the first few days you take it. Then the stool will return to normal. One of my herbal laxatives will do make green stool, too, if I take just enough to loosen the stool without it being diarrhea. Normal solid stool with a dark green appearance can be off-putting unless you realize what the source of it likely was. So, if it's for any of these reasons, you shouldn't be concerned.
Probably something you ate , have you had green veg , like spinach ?