OK...why the sea-foam-green poo?

[Barredhen]

One week ago I started noticing that somebody or a few somebodys has blue/green coating on their poop. Any guess as to why? These pictures make it look less colorful than it is, its quite obviously coated in blue/green. It reminds me of when pennies "turn green" - can't say as I've seen this one.

 

[chickens really]

Normal I'm thinking..What have they been eating?

 

[Barredhen]

That would be good.
Nothing new to them. They're in a 100x100 fence, so grass, weeds, bugs etc, some kitchen scraps and their layer mix.
I've just never seen that color.