To expand on this a bit...
To make an Olive Egger all you need to do is cross a brown egg breed to a blue egg breed. The most popular brown egg breed used is Marans, but any breed that has a brown egg can be used. Same thing with the blue egg breed.
For instance, I currently have 2 different...
You won't be able to tell if it's an Olive Egger until it lays an egg. OEs are a hybrid therefore there is no standard on what one looks like. The only thing that makes it an Olive Egger, is the olive egg.