flying colours vs plural

flying colours and plural both are nouns.

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

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

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