Do you know that the people having blue eyes descend from the single European who has lived in between 6-10 thousand years ago! They develop a special ability the accounts for this iris coloration.
Before this genetic variation, the humans use to have brown eyes. This variation changed the amount of pigments that are produced by the people in their eyes. It caused the shades of brown color. The shades like the hazel, dark brown, light brown, etc.
In fact, after a few years in this scientific research, it was discovered that the cause of blue eyes was the mutation to a separate gene. It occurred first, when the people migrated from Africa to Europe. This implies that every individual having blue eyes must have been descended from the European people.
This proves that, the people having blue eyes are all related to each other.