People with monochromatism see only:

Monochromatism refers to a condition where an individual can only perceive one color or shades of one color. People with monochromatism typically see the world in hues of black, white, and gray. This is because their color perception is limited to the light and dark variations, without the ability to distinguish between different colors. This condition affects the cones in the retina that are responsible for color vision, leading to an absence of color discrimination beyond these shades.

In contrast to the other options, which suggest varying ranges of color perception, the ability to see only in shades of black, white, and gray is intrinsic to monochromatism. Therefore, the correct answer aligns with the definition and understanding of this particular visual impairment.