Animal eyes come in varieties that people simply lack. Owls have golden eyes and cats can have yellow or orange eyes. So who not people?
Eye colour is determined by the colour of the iris which is a ring of muscle in the eye also called a sphincter.
The colour is controlled by melanin. With a lot of melanin, your eye will look brown, as it decreases, your eye may show up as blue, green or hazel.
An animal with orange eyes actually has amber eyes – it’s a variation of brown.
Relatively few animals have red eyes, with the red-eyed tree frog being a notable exception.
Many people think albinos have red eyes, but that’s not true. Albinos lack pigment and therefore melanin. Their eyes appear red because of the blood vessels in the iris.
Eyes sometimes appear to change colours when they dilate because the pupil is wide open and the iris is compressed. It therefore may look darker. On the other hand, when the eye is constricted on a nice sunny day, the iris expands and may look lighter in colour.
No matter what happens with a human eye though, it’s highly unlikely that we would develop the same sorts of colours as cats and owls.
On the other hand, coloured contact lenses technology has evolved to the point where we can have eye shades of almost any colour – at least temporarily.