Olive eggers are laying-type hybrid chickens. They are the result of crossing a blue or green egg layer with a dark egg layer. The resulting pullets can look like either parent or a mixture of the two, making it impossible to look at a bird and say that it is (or isn't)  an olive egger.

Though there are many ways to make an olive egger. not all of them are sexable as chicks. There are ways to create sex-linked hybrids, but we have settled on a hybrid of 2 autosexing breeds as a way to easily sex the chicks.

This picture is of the 2 parent breeds, your olive egger might grow up to look like either parent, or a combination of traits.