Evolution of human colour vision lights, which appear to be clear. Other colour perception issues include having trouble distinguishing yellows from reds and violet, lavender and purple from blue. In other cases, objects that reflect both red and blue light may appear to just be blue to these individuals. Deuteranopes, who are missing medium wavelength sensitive cones, are similar to protanopes in that they cannot distinguish between colours in the green-yellow-red part of the electromagnetic spectrum. However, deuteranopes do not suffer from dimming issues. For example, purple colors are not seen as being opposite to other colours in the spectrum but instead appear to be
Squirrel monkey in the mid-teens. Colour vision in squirrel monkeys has been extensively studied as a stand-in for human ailments. In humans, two genes for colour vision are found on the X chromosome. Typically, one gene (OPN1LW) produces a pigment that is most sensitive to the 564 nm wavelength, while the other gene (OPN1MW) produces a pigment most sensitive to 534 nm. In squirrel monkeys, there is only one gene on the X chromosome but it exists in three varieties: one is most sensitive to 538 nm, one to 551 nm, and one to 561 nm. Since males have only one X