Eye color is influenced by a pigment in the iris called melanin. The amount of melanin determines the color of the eyes. A large amount of this pigment creates dark eyes (black, hazel and light brown), and a smaller amount forms light (green or blue).
Red eye color is found only in albinos. It is associated with the absence of melanin in the iris, therefore it is determined by blood in the vessels of the iris.
The amount of melanin is determined by heredity. There are significantly more dark-eyed people in the world than light-eyed people, and the reason for this lies in the genetic dominance of traits associated with a large amount of melanin. Therefore, if one parent has dark eyes in a family and the other has light eyes, their children are likely to have dark eyes.
Eye color can change throughout life. Sometimes, soon after birth, the color of the eyes changes from light to dark - this is sometimes found in Caucasians, and is associated with the accumulation of melanin in the iris. In older people, the eyes sometimes turn pale, which is associated with a certain loss of transparency of the mesodermal layer. In addition, the color of the eyes may change due to certain diseases.