We are assuming that you are referring to Mute Swan cygnets. First, the taxonomical species name is Mute Swan. However, swan keepers term cygnets that are taupe (brown) in color with dark black feet as being Royal Mutes. White colored cygnets with a taupe colored foot are called Polish Mutes.

Many years ago (decades at least), someone in the Polish/Czech area tried to get an albino swan by repeatedly in-breeding swans until they could get a "white" swan. They succeeded in that they got a leucistic (not albino because the beak and feet have color and an albino would possess no coloring on any body part) color form of the mute swan. This leucistic form was once known as a separate species called cygnus immutabalis, the unchanging swan. However, taxonomists realized that this was not a separate species, just a color variation. Hence the name, Polish mute. The Regal Swan