Monochromacy

Monochromacy, also known as "total color blindness", is a complete inability to distinguish colors. This is distinguished from more common forms of color blindness, in which the affected individual can perceive color differences, but cannot make the same distinctions between colors as can an unaffected person.

Organisms with monochromacy are called monochromats. The perceptual effect of any arbitrarily chosen light from the visible spectrum can be matched by any pure spectral light.