Don't know the reason, but found some chickens to be black in nesting pen (broken texture perhaps?).

Example:

its probably a lighting issue when rendering the model. I make sure the block isn't messing with the lighting at all.

I thought so too, but when I switched them around the gold chicken was visible in the place of the emerald one, and the emerald one was still black in the left nesting pen.

Thats super strange than. No idea. Ill still play around with it.

Found out it was another mod interfering with lighting, no further investigation needed, Thank you!

Thanks.. what mod was it?