What term describes people who see only in black and white?

The term that describes people who see only in black and white is "monochromats." This condition is a form of color vision deficiency, where individuals have only one type of photoreceptor for color vision instead of the usual three. As a result, they cannot perceive colors and see everything in shades of gray. Monochromacy typically arises from a deficiency in cone cells, which are responsible for color detection in the retina.

In contrast, dichromats have two types of color receptors, allowing them to see some colors, but not all—commonly leading to certain types of color blindness where some colors, like reds or greens, may be indistinguishable. Trichromats are individuals with normal color vision, possessing all three types of cone cells and able to perceive the full spectrum of colors. The term "partially colorblind" is more general and can refer to various types of color vision deficiencies, not specifically to seeing only in black and white, thus not capturing the specific condition defined by monochromats.