Actually while this is an excepted theory its also told that the blue coloration was bred many times over and over by some breeders in holland. While the ducks kept being bred some of the offspring began to get darker and eventually became black, this one was the one I've gone bye and is the accepted theory of the BCDC (The British call duck Club)![]()
I haven't read it exactly that way before, but it makes sense if that's how it happened. Blues have genes for black, so if you mated two blue ducks, you should get some self blue, some self black, and some splash. That should give you a path to blacks that breed true in the future generations.