Organisms with monochromacy lack color vision and can only see in shades of grey ranging from black to white.

[1][2] Rod monochromacy (RM), also called congenital complete achromatopsia or total color blindness, is a rare and extremely severe form of an autosomal recessively inherited retinal disorder resulting in severe visual handicap.

People with RM have a reduced visual acuity, (usually about 0.1 or 20/200), have total color blindness, photo-aversion and nystagmus.

A cone monochromat can have good pattern vision at normal daylight levels, but will not be able to distinguish hues.

however, a focus on behavioral and genetic testing of mammals has accumulated extensive evidence of at least dichromatic color vision in a number of mammalian orders.

Marine, nocturnal or burrowing mammals, which experience less light, have less evolutionary pressure to preserve dichromacy, so often evolve monochromacy.

[citation needed] A recent study using through PCR analysis of genes OPN1SW, OPN1LW, and PDE6C determined that all mammals in the cohort Xenarthra (representing sloths, anteaters and armadillos) developed rod monochromacy through a stem ancestor.