Cones within human eyes are sensitive to red, green and blue wavelengths allowing most people, who are trichromats, to see about a million colours.
Take one of those functioning cones away and the number of colour combinations decreases to 10,000. This case is commonly referred to as colour blindness or dichromacy.
Based on the way in which the genetic mutation dichromacy occurs on the X chromosome, researchers investigated the possibility that some people may be able to see more.
Enter the tetrachromats! It’s estimated only 1% of people have a fourth cone and can see 100 million colours.
Take a look at this video for from Discovery News for more detail.