Yeah, we all know that the eye color often is the genetic trait from our mother and father. As usual, black, brown, blue, gray, green, hazel or some combination of colors is the common color of our eyes. If you know a little knowledge about the genetics, I think you should know the combination of the genes. Human eye color originates with three genes instead of two genes, so it is a tough work to figure out the combination result of the genes. Although, we know the colored part of the eye is called the iris, which has pigmentation determining the color of out eyes. At the same time, the iris plays an important in expanding and controlling pupil size, so when we are getting older, the color of eyes will change according to the pupil size. So when you notice your kids' eyes' color changed, just be relax.