Why do chickens lay different-colored eggs?
Genetics is the simple answer to why chickens lay different-colored eggs. Some chickens lay white shell eggs and some lay brown shell eggs, similar to the way hair color varies in people.
Shell color is not associated with the internal components of the egg. If you break a brown egg and a white egg, you can see there’s very little difference between them.
The nutrition of the hen could cause a few minor changes, especially in yolk color, but the color of the egg shell is not related.
From turkey eggs to emu eggs—there’s lots of variation in bird egg colors.
Shell color is not typically determined by a single gene. A previous research study at the University of Wisconsin–Madison showed that multiple genes are involved. Researchers crossed two chickens that laid white eggs, pure lines, and ended up with offspring that laid brown-shelled eggs. They found that different genes were involved with different breeds.
Apart from brown and white, some chickens lay even blue or green eggs. In this case, a single dominant gene is responsible for the blue and green color and traces back to breeds from South America.