Janie, you are spot on with the compostion of the foremilk and hindmilk!

Foremilk is very high in lactose and the more watery part of the milk. the more foremilk he is getting the more his intestines need to work, and he made not be making quite enough of the enzyme that breaks it down - Lactase. In truly lactose intolerant bubs even the smallest bit of foremilk can send their poo to the state that Vixstar is dealing with.

Hindmilk has more fat and less sugars (lactose is a sugar) and is the part that returns the poo to yellow.

Vixstar, try expressing until a few minutes after your letdown as this will take more foremilk than hindmilk, and make sure he stays on until you are empty. you will feel very soft and floppy when you are empty.

Keep an eye on his weight though because if he is struggling with the lactose it can give diahorreah, and mucousy poo. mucousy poo is always a cause for concern, just as much as diahorreah.