What makes some chicken eggs blue?

Five breeds of chickens are responsible for laying blue eggs: Araucanas, Ameraucanas, Lushi and Dongxiang (not popular in America) and Cream Legbars. A study found that a gene called "oocyan" is responsible for the coloring, due to a retrovirus (not harmful to bird or egg eater) that integrates into the genetic code of the bird. #didyouknow