. Heterochromia A term used to describe the difference in a person's eye color. A person with central heterochromia has different colors in one eye. Complete heterochromia occurs when two eyes have different colors. Heterochromia of the eye is due to changes in the concentration and distribution of melanin, a pigment that causes skin, hair and eye color. The word "heterochromia" is derived from ancient Greek, where "heteros" means "different" and "chroma" means "color." These conditions are also known as heterochromia iridis or heterochromia iridum. There are some types of heterochromia in dogs, cats and horses. There are three main types of eye heterochromia.