Chickens sometimes have a running dark green/blackish poop?

[undine]

My chickens get this kind of poop sometimes, andd omgggg they are so hard to clean off after they've harden on surfaces. What kind of poop is this? Are my chickens okaay

 

[Sunsplash]

My chickens sometimes do this too. Here's a poop chat that i got from another forum. I hope it helps you.
http://chat.allotment.org/index.php?topic=17568.0

forum source:https://www.backyardchickens.com/t/761587/bloody-chicken-poop-diahhrea-poop-chart