It happened to DS when he was 3-4 months old.
If the baby is happy and doesn't show signs of discomfort, then I wouldn't worry too much. I had the foremilk/ hindmilk imbalance for a while, but the baby and the breast will sort it out themselves.
Yet, it did happen to me once that his poop was dark green (neon spinach green) for a few days. It WAS something new in my diet (lavender tea). So as soon as I stopped drinking that, his poop went back to normal.
Hope it helps.