multicolored formula poo?

RaeAnt

I've been meaning to ask about this for awhile. DS is on formula and has been from the get go. in the begining it was the light tan with little pebble like chunks. After going to a different formula it became thick dark green with a mix of almost black which we assume is from the iron. Now in the last week he still does the green/black poos buthas added back in the chunky lt. tan poo. Why the difference? Nothing has changed other than his age. Is it just his digestive system maturing?

We plan on asking his pedi about it Friday at his appointment but were curious if anyone else experienced it and what they thought it was or were told.