Is this roo a blue birchen? I do know (and Bev believes this as well) that they key to dark egg color is to start with a roo hatched from a very dark egg. So, I would THINK that if you crossed this boy over the pullets from those light eggs, you'd probably end up with a "4" egg, which is acceptable within the Marans breed. Then, as stated, hatch only the darkest eggs and after a few short years, you should be where you want to be for color.