The iris is the coloured part of the eye and is as individual as a fingerprint. The so-called iris, also known as the eye’s “coloured diaphragm”, can appear in many shades of grey, green, blue or brown due to an individual distribution of pigment.
Regardless of its colour, the iris regulates the amount of light entering the eye through two muscles. Depending on the lighting conditions, it can either constrict or dilate. It functions like a camera aperture: it regulates the incoming light that falls into the pupil—the aperture opening of the eye.
90% of all people worldwide have brown eyes. Alongside grey and blue, green is the rarest eye colour at only 2%. The colour of the iris is genetically determined: the predisposition for brown eyes is the most dominant. As a result, most people have brown eyes, even though babies are often born with blue eyes.