achromatic vs iron-grey

achromatic is not a noun while iron-grey is a noun.

Word	Noun	Adjective	Verb	Adverb
achromatic	No	Yes	No	No
iron-grey	Yes	Yes	No	No

achromatic (noun)	iron-grey (noun)
	the color of freshly broken cast iron

achromatic (adjective)	iron-grey (adjective)
having no hue	of the grey color of iron