Why is there a black circle around the color of your eyes?

The dark circle around the colour of your eyes is called the iris, and it is the coloured part of the eye. The iris contains muscles that control the size of the pupil, which is the black hole in the centre of the eye. The pupil lets light into the eye, and the iris controls the amount of light that enters the eye by changing the size of the pupil.

The colour of the iris is determined by the amount and type of melanin in the iris. Melanin is a pigment that is also responsible for the colour of your skin and hair. People with brown eyes have more melanin in their irises than people with blue eyes.

The iris also contains blood vessels that help to nourish the eye. These blood vessels can sometimes be visible, and they can cause the iris to appear to have a dark circle around it.