Assuming you mean the part surrounding the pupil that people are talking about when they say someone has "brown eyes" or "blue eyes", it's the iris.
The iris
The coloured part of your eye is called the iris.
the cornea is the coloured part of the eye
The iris is the coloured part of the eye.
The coloured (or pigmented) part of the eye is the iris.
The iris is the coloured part of the eye.
the coloured part of the part of the eye
The Iris
An Iris is a flower as well as part of the eye (it is the coloured ring around your pupil).
The coloured part of the eye is the iris.
The iris is the coloured part of the eye, but it's the pupil that narrows and widens.
The coloured section of your eye is called the 'iris'. And the black circular ring is called the pupil.