Foot color is not indicative of male or female, although if the swan keeper notices the difference in color, then he/she can obviously distinguish the genders by this particular characteristic.

Black feet in mute swans means that the swan is a "royal" mute and taupe or light colored feet means that the swan is a "polish" mute. There really is no species term as royal or polish, only swan keepers use this as a clarification of a leucistic coloration.

Many years ago, possibly centuries, someone in Poland or Eastern Europe tried to get an albino swan. They kept breeding and inbreeding until the color was supposedly removed. Once the colorless or changeless swan was developed, there was even an attempt to make it a species called "immutabalis" the changeless swan. However, taxonomists later determined that it was only a leucistic coloration not another species. Because there is still a light foot coloration as well as a lighter beak coloration, the swan could not be deemed albino which would mean an all white swan (feet as well as beak).

Sometimes, just like people, if there is a change in temperature especially water temperature, or insufficient circulation, the feet may get darker or lighter. This may account for the changing color in the swan's feet. The Regal Swan