So do you cull the cockerels at hatch?Strange thing.... I got some chicks from her and they lay a nice BROWN EGG. No blue color at all! I have an unrelated roo over them so I hope he is not carrying the green egg genes. Blue eggs are DOMINATE so I know the girls just didn't get that from the dams or sires. They autosex really well at hatch too. I have not had any issues sexing them, I am selecting for darker pullets and roos to improve the autosexing in the next gen.
My roo is about 9 months old and is a good size roo but I can't help you with a good age to harvest roos.... I just don't do that yet, don't have the space or time to grow them out.