Hello David

We need a bit more information, then maybe one of the health experts can help out. Personally I don't know about chicken poop, but I know I've seen all sorts of colors in it, usually dependent upon what they've eaten. If they eat mullberries, I see purple poop for days LOL. Answer these, please, and I'll tag a few folks who might know:
Where are you located?
What kind of food are you giving them? Also treats, etc.
How old are they?
How much area do they roam about? Just their run, or do they free-range?
@Wyorp Rock @casportpony @azygous