Barbara Marquand is a staff writer at NerdWallet, a personal finance website. Email: bmarquand@nerdwallet.com. Twitter: @barbaramarquand.
The eye may change color due to alteration of genes in the cells of the iris. This is because of your DNA factors in the body. The gene alteration can cause the eye to change color from brown to green and vise verse. There is no any explanation to the cause of the genes behaving in these manner. Prolonged exposure to the sun might also be another cause that made my eyes to change the color.
Eye color is the result of variations in the amount of melanin, a pigment found in the front part of the iris of the eye. The lack of this pigment results in blue eyes, some pigment gives green and lots of pigment gives brown eyes. So light brown eyes just have a bit less melanin than darker brown eyes. All of the different shades of eye color happen the same way. Blue-green eyes have an amount of melanin between green and blue, hazel eyes have an amount of pigment between green and brown, etc.