While you might think that it all comes down to colour, the researchers found that two other factors are key - pupil size, ...

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 pupil is the opening located in the center of the iris of the eye. It controls the amount of light that enters the eye so that you can see clearly. The pupil size is controlled by muscles of ...