I have two Barred Rocks hens and a bunch of Orpingtons of varying ages and colours: Black, Buff, Blue, and Lavender or Gray. I'm used to seeing light brown eggs. Imagine my surprise at finding a blueish green egg this morning! The farmer I bought my most recent batch of pullets from said they were all purebred Orpingtons, but he must have been wrong. They certainly all look like normal Orpingtons... Is it possible that one of my hens is a cross, even though she doesn't look it?