All of my Bielefelder hens and pullets are the color of the one on the bottom. So I have never tried to breed for a darker color. I do have two young roosters one is darker the other lighter. If I were you I would try and breed to a Rooster with darker base tones. They are not as common; most Biele roos have a silver/gray base when young and as they mature all the other colors come in and they develop the Crele pattern. I think that would be your best chances and this is only a guess. You would actually need to see what color hens the rooster you breed too produces to be exact.
Thanks TN, I will have to wait and see then.