dress blues vs plural

dress blues and plural both are nouns.

Word	Noun	Adjective	Verb	Adverb
dress blues	Yes	No	No	No
plural	Yes	Yes	No	No

dress blues (noun)	plural (noun)
a dress uniform for formal occasions	the form of a word that is used to denote more than one

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