The prevalence of different eye colours varies across populations. Worldwide, brown is the most common eye colour while the least common eye colour is green.
Melanin is a pigment which is responsible for eye colour and each person's eye melanin content is genetically determined. People who have high amounts of melanin in their irises have brown eyes while those with blue eyes have little or no melanin in theirs.
Other eye colours are hazel, blue, silver and amber.