off-white vs achromatic

off-white is a noun but achromatic is not a noun.

Word	Noun	Adjective	Verb	Adverb
off-white	Yes	Yes	No	No
achromatic	No	Yes	No	No

off-white (noun)	achromatic (noun)
a shade of white the color of bleached bones

off-white (adjective)	achromatic (adjective)
of something having a color tending toward white	having no hue