Yes, Its perfectly fine. My baby is 7months old.He too use to makes potty of green colour muddy like , but its ok.After digestion our potty is also green in colour but since it stays for long hours in our intestine it changes colour to yellow/brown etc. since baby have short intestine in length the potty comes out earlier and doesnot stay long in the stomach so its green as it comes out. Its perfectly normal. Nothing to worry