The mute swan cannot produce a black cygnet because these are two different species of swans. However, the coloring of a cygnet from a mute parent can be a very dark gray color which signifies that it is what is known as a Royal Mute (black feet) as opposed to a Polish Mute (light colored feet and the cygnet is white in color). Polish mutes are produced by a leucistic coloring in the genes. It is not an albino but a whiter colored swan. Hope this helps. The Regal Swan