Does feeding a 12-week-old baby with Lactose-free formula cause dark green stools?

Hi doctor,

I want to ask about my baby. She is 12 weeks old now. The baby is fed with Lactose-free formula, and her stools are dark green or greenish-tan. Sometimes can see yellow color mixed with green. Sometimes her stools are soft, and sometimes it is harder. She poops once or twice a day. She feels well and eats well. We changed the formula with a doctor's advice because her stools were runny with mucus and had a bad smell. She pooped very often, and she ate a small amount of formula. She had no rash and no vomiting. So, I would like to ask if it is normal if baby poops are green, and when can we return to the normal formula?

Thank you.