The color of the iris is determined by heredity. In today's world, dark-eyed people much more than light-eyed. This is due to the dominance genetic trait which is responsible for high levels of melanin. Therefore, children with parents, one bright-eyed, and the other - dark-eyed, will, most likely, dark-eyed.
In blue eyes iris outer fibers characterized by a low density and a low content of melanin, the fibers and the inner layer differ in dark blue. The iris becomes blue, if whitish fibers of the upper layer are arranged densely and "diluted" the blue color of the lower layers of the iris. Gray eyes structurally similar to blue, but the density of the fibers in the outer shell are higher. In addition, the gray eyes can often be areas with different melanin content: green, yellow and brown streaks. In this case, the eye color is determined by what shade of color predominates in the iris in daylight.
Green color of the iris is often associated with red hair gene. This leaky characterized eye color or light yellow-brown iris fiber outer layer, which in combination with the inner layer gives a blue green color. Hazel and brown eyes, sometimes called amber are rare and different prevalence in the outer layer of the iris of closely spaced fibers yellow and brown. Iris hazel color saturated melanin. The more melanin contained in the upper fibers of the iris and the tighter they are, the darker iris, but its color is brown and never goes to black.