What is the primary function of the iris in the eye?

The primary function of the iris in the eye is indeed to give the eye its color. The iris is the colored part of the eye, and it consists of muscle fibers that help control the size of the pupil, which in turn regulates the amount of light that enters the eye. The variation in pigmentation within the iris is what specifies the color of an individual's eyes, whether they be blue, brown, green, or any other shade.

While the iris does play a role in vision by controlling light intake, which indirectly aids sight, its most defining characteristic and role is related to the pigmentation that contributes to the eye's color. This function helps to create the aesthetic aspect of eyes as well as plays a biological role in signaling health and genetic traits in many species.