Poop question

[Squirreler]

I have two gray squirrels (almost 5 weeks old) exclusively on fox valley. One just started having black poop (well formed, no diarrhea). I just don't ever remember a change in poop color with previous babies until I started with healthy blocks.

[SammysMom]

Although i am not sure of the answer to yiur question, a pic of the two different poops might help to answer it.