monochrome vs colourful

monochrome is a noun but colourful is not a noun.

Word	Noun	Adjective	Verb	Adverb
monochrome	Yes	Yes	No	No
colourful	No	Yes	No	No

monochrome (noun)	colourful (noun)
a black-and-white photograph or slide
painting done in a range of tones of a single color

monochrome (adjective)	colourful (adjective)
having or appearing to have only one color	having much or varied color
	striking in variety and interest
	having color or a certain color; sometimes used in combination