A Mexican hen named Rabanita has become quite an attraction in the village of Cuautitlan since she started laying green eggs last month. Apparently the hen, owned by Elvira Romero, eats a regular diet. From the Associated Press:
Scientists believe that shell colour - which does not affect the colour or flavour of the yolk or white - is determined by the genes, and say blue or green shells are frequently found in the Araucana chicken strain.Link
Green egg layers attract a premium in some parts of South America, where poultry breeders aim to produce chickens, which lay nothing else.