Diarrhea and change formula

Hi. My lo 11months had an episode of diarrhea last 2 weeks. I switch to isomil and he recover for few days. I slowly switch to formula but it started again like he poop 4x in a day yellow watery poop. Then i immediately switch back to isomil and seems the diarrhea stop. Just soy milk havent started back with formula till today. But hes poop is green colour instead of yellow watery poop. Is that normal? Any mummies had experienced the same too?