People who have, for instance, both protanopia and tritanopia are considered to have cone monochromacy.

A rarer form of color blindness is tritanopia, where there exists an inability to perceive short wavelengths, such as blues.

For tritanopia, the S-opsin gene must be introduced instead of M-opsin gene.

Those with tritanopia and tritanomaly have difficulty discriminating blueish versus yellowish hues.

Nope, colorblind people won't have a tough time at all, I test all of our colors for deuteranopia, protanopia, and even tritanopia.

Simulation of US 4-color map as seen by color-blind person with tritanopia (a rare form of color-blindness).

Although the name is Blue-yellow color blindness (tritanopia), people affected by this type of color blindness can usually tell the difference between blue and yellow.

Dichromacy (tritanopia)

Less common forms of dichromacy include protoanopia (lack of L-cones), and tritanopia (lack of S-cones).

Color blindness involving the inactivation of the short-wavelength sensitive cone system (whose absorption spectrum peaks in the bluish-violet) is called tritanopia or, loosely, blue-yellow color blindness.

While red/green color blindness among deuteranopes can be treated by introducing M-opsin genes, rarer forms of color blindness such as tritanopia can in principle be treated as well.