How do people get one colour in one eye and a different one in another eye?

Question: How do people get one colour in one eye and a different one in another eye?
- Keywords:
  eyes
Asked by Danielg to Adrian, Gaia, Jim, Scott, Vicky on 7 Mar 2016.
- Gaia Andreoletti answered on 7 Mar 2016:
  
  People with different eye color (heterochromia) is a result of the relative excess or lack of melanin (a pigment). This characteristic may be inherited, or caused by genetic mutations within genes determining the eye colors or by an injury.

Question: How do people get one colour in one eye and a different one in another eye?