A mutation occurs in one of the genes that codes for the eye color of an individual. This mutation changes the color of the eye from black to dark brown. The eyesight of the individual remains normal. What kind of mutation is this, and why?

A. Beneficial mutation; changing eye color gives an advantage for finding food.

B. Harmful mutation; changing eye color causes health problems.

C. Harmful mutation; changing eye color increases reproductive success.

D. Neutral mutation; changing eye color has no effect on vision.