monochrome n.

Proto-Indo-European root meaning "small, isolated."

It forms all or part of: malmsey; manometer; monad; monarchy; monastery; monism; monist; monk; mono; mono-; monoceros; monochrome; monocle; monocular; monogamy; monogram; monolith; monologue; monomania; Monophysite; monopoly; monosyllable; monotony.

It is the hypothetical source of/evidence for its existence is provided by: Greek monos "single, alone," manos "rare, sparse;" Armenian manr "thin, slender, small."

in reference to color, "intensity of distinctive hue, degree of departure of a color-sensation from that of white or gray," 1889, from Latinized form of Greek khrōma "surface of the body, skin, color of the skin," also used generically for "color" and, in plural, "ornaments, makeup, embellishments," a verbal noun from khroizein "to color, stain, to touch the surface of the body," khrosthenai "to take on a color or hue," from khros, khroia "surface of the body, skin."

Beekes considers this noun to be of uncertain origin. It sometimes is explained as being somehow from PIE *ghreu- "to rub, grind" (see grit (n.)).