Iris (eye)

The iris (plural: irides or irises) is a thin, circular structure in the eye. It controls the diameter and size of the pupils.
Eye colour is the colour of the iris. In humans, the iris may look green, blue, brown, hazel (a combination of light brown, green and gold), grey, violet, or even pink. In response to the amount of light exiting the eye, muscles attached to the iris expand or contract the pupil. The larger the pupil, the more light can enter the eye and reach the retina.