In anatomy, heterochromia (ancient Greek: ἕτερος, héteros, different + χρώμα, chróma, color) is a difference in coloration, usually of the iris but also of hair or skin. Heterochromia is a result of the relative excess or lack of melanin (a pigment). (wikipedia)
The fascinating two colored eyes photos:

Mila Kunis

josh henderson

Demi Moore

Kate Bosworth
What are your thoughts?