A black copper marans can HIDE the wheaten gene. They are still marans but aren't pure black coppers. When two birds carrying the recessive wheaten gene are paired up, there is a chance that some of the chicks will inherit two copies of the wheaten gene and will then be visibly wheaten as a chick. Also, your chicks that look black may or may not be carriers of the wheaten gene. When there is only one copy, you can't see it in the chick down.