polychrome vs colourful

polychrome is a noun but colourful is not a noun.

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

polychrome (noun)	colourful (noun)
a piece of work composed of or decorated in many colors

polychrome (adjective)	colourful (adjective)
having or exhibiting many colors	having much or varied color
	striking in variety and interest
	having color or a certain color; sometimes used in combination

polychrome (verb)	colourful (verb)
color with many colors; make polychrome