Colorful diaphragm WSJ Crossword Clue

Think of a garden of hues that also controls the light entering a room.

The ???? is the colored part of the eye surrounding the pupil.

The clue uses 'colorful' to hint at the variety of colors associated with the ????, which is the part of the eye that controls the diameter of the pupil. The word 'diaphragm' is a play on words, as it refers to the ????'s function of regulating light, similar to a camera diaphragm.

Eye structure controlling pupil, Eye part around the pupil, Something you can see right through, Colored part of the 59-Down, Pupil's surroundings