They can't lay white eggs. Turns out mine wasn't a pure breed either in the end. But I don't have her anymore because she was killed last year by something, I think rather a stoat, sparrow hawk or a buzzard.
I have a cream legbar who lays white eggs, people on a facebook group are now saying "she is not a pure breed, she is a cross" and it is really starting to get on my nerves, can she lay white eggs or does this mean she isn't a pure breed?