Chickens lay green eggs because of the pigments they deposit on the shell during egg formation. The green color comes from a combination of blue and brown pigments. Specifically, a pigment called oocyanin, which penetrates the shell and colors it blue, is deposited early in the shell formation process. Then, a brown pigment called protoporphyrin is added on top, resulting in the greenish color on the outside. This happens in certain chicken breeds genetically predisposed to lay blue or green eggs, such as Ameraucana, Araucana, Easter Egger, Cream Legbar, and Olive Egger. The green eggshells are blue on the inside due to the oocyanin pigment underneath the brown overlay. The genetic combination of breeds that lay blue eggs crossed with breeds that lay brown eggs produces the green hue. In sum, the green eggshell is a natural phenomenon linked to the hen's genetics and pigment deposits during egg formation.