IS question

In fact, all human beings have pupils which are certainly black in colour in spite of the colour of their iris.

Iris colour shows eyes have different colours. But pupils are black because of our retina. Our retina are consisted of several layers which one is choroid. Choroid is black in colour, it is very important in preveting light reflection occurs in our eyes. When light ways come into our eyes, the black pigment on it will absorb the light ways and therefore we can see things clearly. If there is no choroid layer in our eyes, things will be see in blurred.

The black pigment in choroid hence explained why our pupils are always appear to be black.