We used NAN HA in the beginning (and now regular NAN Pro) and C's poos were quite a dark olive-y green. They didn't really change till we had almost given up BF altogether. It's a totally normal colour for some formulas - all my friends' bubs who were on HA formula had the same colour poo

As soon as we switched to the non-HA stuff his poos changed to a more "normal" colour (yellowy brown) and stayed like that till he went on to solids. Don't ask me what they're like now