<P> Eye color, specifically the color of the irises, is determined primarily by the concentration and distribution of melanin . The affected eye may be hyperpigmented (hyperchromic) or hypopigmented (hypochromic). In humans, an increase of melanin production in the eyes indicates hyperplasia of the iris tissues, whereas a lack of melanin indicates hypoplasia . The term is from ancient Greek: ἕτερος, héteros meaning different and χρώμα, chróma meaning color . </P> <P> Heterochromia is classified primarily by onset: as either genetic or acquired . Although a distinction is frequently made between heterochromia that affects an eye completely or only partially (segmental heterochromia), it is often classified as either genetic (due to mosaicism or congenital) or acquired, with mention as to whether the affected iris or portion of the iris is darker or lighter . Most cases of heterochromia are hereditary, caused by certain diseases and syndromes . Sometimes one eye may change color following disease or injury . </P> <P> In segmental heterochromia, sometimes referred to as sectoral heterochromia, areas of the same iris contains two completely different colors . </P> <P> Segmental heterochromia is rare in humans; it is estimated that only about 1% of the population have it . </P>

What does it mean when you have two different coloured eyes