Question: Why are some of us colour blind?

Steven Gardner answered on 20 Jun 2013:

There are two types of light receptor cells in your eye, called rods and cones. The rods are mainly responsible for your peripheral vision and low light vision. There are three types of cones and their job is to detect the three primary colours (Red, Green and Blue). Colourblindness is where the cones in the eye don’t work properly, so you struggle to distinguish colours (most often red and green).