flying colors vs plural

flying colors and plural both are nouns.

Word	Noun	Adjective	Verb	Adverb
flying colors	Yes	No	No	No
plural	Yes	Yes	No	No

flying colors (noun)	plural (noun)
complete success	the form of a word that is used to denote more than one

flying colors (adjective)	plural (adjective)
	grammatical number category referring to two or more items or units
	composed of more than one member, set, or kind