- An Overview of Colour Blindness

There is a common misconception that colour blindness means only seeing in greyscale. This can be the case with some forms of colour blindness, but is rare, and it is much more common to only have some colour perception impacted. Human eyes work with rod and cone cells. Rods largely handle peripheral vision and low-light vision, while cones handle vision in well-lit situations and colour perception.

Humans have three classes of cones (trichromacy), each of which is sensitive to a different wavelength of visible light. L-cones are most sensitive to green through yellow to red, M-cones to green through yellow, and S-cones to blue. There is overlap between what colour each cone sees – especially the M and L cones.

Below are demonstratory figures of the effects of various colour blindness. They do not represent all people’s experiences with colour blindness and are representations only. Complete blindness (ending in -opia) is shown here, though partial cone dysfunction (ending in -omaly, like protanomaly or deuteranomaly) is not. The majority of people with colour blindness are have only partial colour deficiency.

A wet rock with pink and orange hues with plants around it. In the background are green leaves and in the foreground are purple leaves.
The base photo, unfiltered.
The same image, however the green is now yellow and the purple leaves are now a very grey purple/blue
Protanopia. Red-green colour blindness caused by non-function of L-cones. Often difficult to distinguish blue/purple and green/yellow.
The same image with a very similar colour palette.
Deuteranopia. Red-green colour blindness caused by non-function of M-cones. Similar effect to protanopia.
The same image, however orange/yellow now appears a red-pink hue and the leaves appear a desaturated aqua.
Tritanopia. Blue-yellow colour blindness caused by non-function of S-cones. Often difficult to distinguish greens and blues, and yellow often appears pink.
The same image, though now completely in greyscale. Reds are dark and blues/greens are light.
Achromatopsia. Non-function of all three cones causing monochromatic vision.
The same image, though now steeped in blue. Except for green, colours are extremely difficult to distinguish.
Blue-cone Monochromacy. Non-function of L and M cones.

Achromatopsia and blue-cone monochromacy especially are usually paired with severe photosensitivity and reduced vision. Globally, it is estimated that ~4.5% of males and ~0.6% of females are colour blind. Ethnicity has a large influence on these figures. Red-green colour blindness is the most common by a significant margin (~95% of all colour blindness).

Remember, no two people’s eyes are exactly the same. Different people have different vision and might have colour vision deficiency paired with other conditions.