Personally, I don't think green eggs refer to the color of eggs, but to the eggs laid by hens raised in a green environment. For example, in rural areas, chickens can be seen everywhere foraging in the grass. They eat natural grass seeds, insects and drink water exposed to the sun. They haven't eaten instant feed with various additives, so the eggs laid by hens in this state are all green eggs.

I hope my answer can help you.