Protanopia, in which seeing and distinguishing between colours within the green-yellow-red section of the spectrum is impossible, Dueteranopia which means sufferers struggle to see green-yellow-red, and a rare type of colour blindness, tritanopia, which means sufferers can't see blue-yellow. read more
For example, a red/green colour blind person will confuse a blue and a purple because they can’t ‘see’ the red element of the colour purple. See the example of pink, purple and blue pen cases below to understand this effect. read more