The iris is the colored part of the eye that surrounds the pupil. It controls the amount of light entering the eye by adjusting the size of the pupil. The iris contains muscles that contract or relax in response to light conditions, helping to protect the inner structures of the eye. The color of the iris varies among individuals and is determined by genetics. Common colors include brown, blue, green, and hazel. The unique patterns and colors of the iris can also be used for identification, as no two irises are exactly alike, making them useful in biometric systems.