Which structure gives the eye its color?

The iris is the structure that gives the eye its color. It is a thin, circular structure located behind the cornea and in front of the lens. The pigmentation in the iris, which can vary from person to person, determines the color of the eye, whether it be brown, blue, green, or hazel. The varying amounts of melanin present in the iris contribute to these different colors. Additionally, the iris plays a crucial role in regulating the amount of light that enters the eye by controlling the size of the pupil, thus also contributing to vision but primarily functions in aesthetics and unique identification.

The pupil, in contrast, is the opening in the center of the iris and does not have color itself; instead, it allows light to enter the eye. The ciliary body is responsible for the production of the aqueous humor and the accommodation of the lens but does not contribute to eye color. The cornea, which is the transparent front layer of the eye, has no pigmentation that contributes to the eye's color. Therefore, the iris is the correct answer as it directly influences the visible color of the eye.