A baby's eye color is determined by a polygenic process, according to BabyMed, but predicting the color before birth is not an exact science. Polygenic means "many genes," which means that a baby's eye color is a combination of hereditary gene traits from both sides of the family, rather than being a simple combination of recessive and/or dominant genes from the biological parents, states Family Education.
Two parents who have brown eyes can have a child with brown, blue, green or hazel eyes. Eye color is determined by a pairing of recessive and dominant genes, but since each parent contributes two genes, many different combinations are possible, and hidden recessive genes in combination can produce some surprising results, explains Family Education.
To make matters even more interesting, a newborn baby's eyes often change appearance between birth and the age of three, although eye color can be determined with a fair degree of certainty in many children by the time they are six to nine months old, informs BabyMed. A fairly simple grasp on genetics can help to determine a baby's chances for a specific eye color even if there will be no way to determine it with complete accuracy until the baby has at least reached the age of six months.