How many colours can a person see with monochromatism?

A person with monochromatism typically sees the world in shades of gray, as this condition is characterized by the absence of color vision due to the lack of functioning cones in the retina. Monochromats generally perceive only one color wavelength, leading to a limited visual experience that includes variations in brightness but no discernible colors. Therefore, they can see essentially only one "color," which is the intensity of light rather than true color differentiation.