The percentage of the world's population who have multiple-colored eyes is not documented. Most babies are born with blue eyes that vary in color but develop into a permanent shade by the age of 5.
Multicolored eyes can be caused by trauma during or after child birth, eye-pigment development failure, genetic disorder, freckle on the iris, inflammation or Horner's syndrome. The color of a person's eyes is passed down genetically. Blue eyes are passed down through English, Irish and Northern European ancestry. Green eyes are found predominantly in people with German, Icelandic and Celtic ancestry. Brown eyes are the most common eye color in the world.