I was born with really dark brown eyes, but as I grew older my eyes started changing. They're now green and it's odd because my mom has dark brown eyes (as she is Asian) and my dad has blue eyes. No one has green. I never understood that change..
It depends on your racial genetics. I believe an albino's eye pigment or lack of it would be. Some people have each eye a different colour. David Bowie comes to mind. If you want really rare eye colour you can get coloured contact lenses.