The eye colours are usually categorized as blue, grey, brown, amber, green or hazel (some classifications also include red, as albinism can produce this). There is a chart called the Martin-Schulz scale which is used to describe different eye colours and their variations. This scale divides eye colours into light, dark and mixed as well as identifying individual colours.

Different eye colours are more common in different parts of the world. Brown is the world's most typical eye colour, as it is found all over Asia and much of the Middle East and Africa, as well as existing to some extent in most other places. Black eyes don't really exist, though some browns are so dark as to appear black.

The 'violet eyes' that you sometimes read about don't really exist either, except as a variant of the red eyes that can go with albinism. But very dark blue eyes can appear violet in certain lights.