My lo had green poo for the longest time, drs and hvs not at all bothered, I did a lot of reading and foremilk/hindmilk imbalance always came up but I was sure it wasn't that for us as lo always fed for a decent length of time and there was no change when block feeding.
At our LLL meeting this week we discussed fore/hind milk imbalance and apparently a true imbalance is very rare. All mums are different, some have a lot of foremilk, others much less, so for some women even a short feed will include lots of hindmilk for baby. Also, babies apparently are amazingly smart and actually control their calorie intake, so if they get a lot of foremilk they will feed longer and if they're getting plenty of hindmilk they will feed for shorter periods (cool, right?) Our group leader told us that in all her years being a breastfeeding counsellor she'd only every met 1 woman with a true fore/hind milk imbalance (of course there may have been others who had induced an imbalance by doing timed feedings etx but these cases were easily remedied by letting lo feed on demand and stay on the breast as long as they wanted)
I gave up trying to work out what made los poo green, I figured if she was happy and healthy and gaining weight well and medical professionals weren't worried then it probably wasnt an issue, and eventuallu poos returned to normal. Having done more reading since i think it was a secondary lactose intolerance (only a temporary thing) caused by antibiotics and thrush meds that she was on for several weeks as a tiny baby. Has your lo been ill or been on any meds that could have upset the balance in the gut?