What is pigment?
|Brown eye colour|
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.