Colour blindness. Image 2 of 2. Fruit and vegetables as seen by someone with deuteranopia, a form of red-green colour blindness. This is due to a deficiency in the 'green' cone cells of the retina. There are three types of cone cells for human colour vision, named after the colours to which they are most sensitive: green, red and blue. Red and green are very close in the spectrum of colours, and losing either the red or green cone cells loses most of the sensitivity to both red and green. Oranges appear the same colour as yellow peppers, red and green peppers look alike, and green vegetables appear brown. Image M450/262 shows this view in normal colour vision.