While you might think that it all comes down to colour, the researchers found that two other factors are key - pupil size, and iris brightness. In their study, the team asked people to rate photos ...

The part that we can see is only just the front. That coloured circle is called the iris and the black spot in the middle is the pupil. This is the part of the eye that lets the light in.

The uvea is made up of a layer of blood vessels, a muscular ring that surrounds your pupil, and the iris, the colored part of your eye. Together, they help your eyes focus so you can clearly see ...