Why is the iris a certain color?
So the color of the iris is determined by the amount of melanin along with its distribution.
Why Does the Iris Have Melanin?
There are multiple different reasons why the iris has melanin, but mainly this is a genetically developed trait over a span of thousands of years.
Genetic Determination - The presence and amount of melanin in the iris are controlled by genes, this melanin is produced by specialized cells called melanocytes located in the iris.
Can it change naturally over time? - Very Unlikely
During fetal development, the amount of melanin deposited in the iris determines its final color.
So Really, Why Are Some People’s Eyes Brown, Blue, Green, or Other Colors?
Brown Eyes: Have a high concentration of melanin in the iris, leading to a darker appearance. The dense melanin absorbs most light, making the eyes appear brown.
Blue Eyes: Have very little melanin in the front layer of the iris (stroma).
Green Eyes: They have a moderate amount of melanin along with a yellowish pigment called lipochrome. The combination of low melanin and light scattering produces green eyes.
Other Variations: Eye colors like hazel or gray are due to variations in melanin levels and light scattering effects.