Yes, this is a common occurrence. Scientifically, all Mute Swans are known as Mute Swans or Cygnus olor. However, due to a color variation, swan keepers call them either Royal Mutes or Polish Mutes.

Centuries ago, someone in Eastern Europe wanted to have an albino swan and tried to produce one by constantly inbreeding his/her swans until a whiter swan was produced. At one time, some researchers thought it was a new species and called it Cygnus immutabalis or the changeless swan. In fact, this was not a new species nor was it albino (without color pigmentation). The new color produced is known as a leucistic coloration meaning there is a variation in the genetic material that produced the color from constant inbreeding. Because many swans have this gene, even today, the coloration can be produced in breeding Mute Swans if one or both carry the recessive gene.

A Royal Mute Swan will have black feet and legs with an orange/red bill. If the cygnets are royal mutes, they will have black legs and feet and will be taupe/grey in color. They will turn white at approximately 6 months of age under the wing and then will turn full color at 1 year of age. The bill will be dark colored until they reach 1 year of age and then it will turn the traditional orange/red color.

A Polish Mute Swan will have taupe/coral colored feet and legs with an orange bill. If the cygnets are polish mutes, they will have taupe/colored feet and legs throughout their lives. Additionally, they will be white, from the time of hatching until the time of their death. So, they will already have the white coloring prior to the normal age of one year. Hopefully, this explanation is beneficial. The Regal Swan