The iris is the colored portion of the eye. Its name is derived from the Greek goddess of the rainbow, due to the many possible colors of the iris. The iris is also a muscle, which controls the diameter and size of the pupil. The pupil is a hole in the center of the iris. It appears black because light rays entering the pupil are mostly absorbed by the tissues inside the eye directly.
The pupil gets wider in the dark but narrower in light.