after taking a closer look at the Columbian Rock birds I do agree most of them are wheaten based, while most columbian wyandottes are brown(eb) based..
Tim the extra eumelanin on their saddle(on columbian wyandottes) is due to eb right?
here is a light sussex(wheaten columbian) rooster with no visible saddle eumelanin(on the right) and a columbian Wyandotte with visible saddle eumelanin
I have not read any research manuscripts or conducted any breeding experiments that would indicate that the brown allele and the wheaten allele act differently , with respect to black in the saddle hackles, when columbian restricted. I am not saying it does not but I can not answer with a yes.