Its not solid black ducks that turn white, its Cayuga that turn white. Muscovy will take a few years to "color" as if they are going to have a white head, they won't be born with it. I have some that are still changing with every molt and they were spring babies. However, if they are blue.. black.. what ever, thats what they will be as a rule. They don't gray, or age like a Cayuga. Only the Cayuga has what would be in human terms, the "gray" gene or the gene that allows them to turn lighter with age.