Heterochromia is a difference in coloration due to the production and concentration of melanin that can affect the iris, hair, or fur, and skin. When it affects the iris it can be complete, resulting in an eye colored differently from the other, or sectoral, when the same iris has two distinct colors.
Luna, a fabulous mongrel dog based in Moscow, Russia, has sectoral heterochromia iridium, and her left eye is half light blue and half brown, resembling a crescent moon. Her right eye, on the other hand, is completely light blue. As we can see from her face, heterochromia slightly affected her fur too.