What would happen to a colour vision if one of three types cones in his or hers eyes stopped working?

The loss of function of one type of cone cell in the eye, a condition known as cone monochromacy, would result in colour vision deficiency or colour blindness. The specific effects would depend on which type of cone cell is affected:

Loss of Short-Wavelength Sensitive (S) Cones (Protanopia):

- Inability to distinguish between red and green colours.

- Difficulty seeing shades of red and green, especially in low light conditions.

- Red and orange colours may appear as shades of brown or grey.

- Reduced sensitivity to blue light.

Loss of Medium-Wavelength Sensitive (M) Cones (Deuteranopia):

- Inability to distinguish between green and red colours.

- Difficulty seeing shades of green and red, especially in low light conditions.

- Green and red colours may appear as shades of brown or grey.

- Reduced sensitivity to red light.

Loss of Long-Wavelength Sensitive (L) Cones (Tritanopia):

- Inability to distinguish between blue and yellow colours.

- Difficulty seeing shades of blue and yellow, especially in low light conditions.

- Blue and yellow colours may appear as shades of grey or white.

- Reduced sensitivity to violet and purple light.

Cone monochromacy is a rare condition, with protanopia and deuteranopia being the most common types. People with cone monochromacy typically develop strategies to adapt to their colour vision deficiency, such as relying more on context and brightness cues to distinguish objects.