The iris is the colored part of the human eye. It forms a ring around the pupil and controls how much light enters the eye by changing the pupil’s size.
The iris contains tiny muscles that contract or relax in response to light. In bright conditions, the pupil becomes smaller; in dim conditions, it opens wider. This is why the pupil is not the colored part—it is the dark opening in the center of the iris.
Eye color depends mainly on the amount and distribution of melanin in the iris, along with the way light scatters through its tissues. Brown, blue, green, gray, and hazel eyes result from different combinations of pigmentation and structure. The cornea is the transparent outer covering at the front of the eye, while the retina is the light-sensitive layer at the back. These parts are essential for vision, but neither determines the visible eye color.