What colored part of the human eye controls how much light passes through the pupil?
The iris is a ring of muscles, located within the colored part of the human eye. The iris controls the process of expansion or constriction of the pupil, which is just a hole in the center of it. That is happening in dependence to the amount of the light coming into the eye. So, when the pupil is expanding or contracting, all the job is done by the iris. Each person has a different iris, which have even more unique characteristics than a finger print (40 compared to 256).