Pigment, lipochrome, eumelanin and eye colour

What is pigment?

Brown eye colour

Pigment is something we all find in the human eyes. The type and amount of pigmentation in the iris determines the colour. There are two types of pigment cells. The first type is called eumelanin and the second one is called pheomelanin (or lipochrome). When you have a lot of eumelanin pigment cells, chances are high you have brown eyes. When your stroma (iris) contains only a small amount of the eumelanin cells, chances are high you will have blue eyes.

Eumelanin and pheomelanin

Most people have a lot of eumelanin cells in their stroma (iris). This means most people on our planet have brown eyes. Dark brown eyes have more eumelanin than light brown eyes. When someones has only a tiny bit of eumelanin, eyes turn blue. Pheomelanin is a little bit different than eumelanin. Pheomelanin creates a pink / red hue. This type of melanin is found in large quantities in red hair. Pheomelanin is also responsible for the third eye colour: green eyes. 

Bradley Cooper's blue eyes

Green eyes and pheomelanin

Pheomelanin not only creates a pink / red hue but also a yellowish hue. We see this colour when a person has a huge amount of pheomelanin inside the stroma. This yellowish colour is called amber. Amber is extremely rare. When a person has both pheomelanin and a little bit of eumelanin, green eyes will form. 

No pigment: red eyes!

Red eyes are very rare. You will only see them when a person has very little pigmentation in the skin, hair and iris. In almost all cases a person with red eyes is also albino: very light (white) hair and skin. Red eyes look red because you see the reflection of blood.