navy blue vs navy

navy blue and navy both are nouns.

Word	Noun	Adjective	Verb	Adverb
navy blue	Yes	No	No	No
navy	Yes	No	No	No

As nouns, navy blue and navy are synonyms defined as:

Other synonyms of navy blue include dark blue.

navy blue (noun)	navy (noun)
a dark shade of blue	a dark shade of blue
	an organization of military vessels belonging to a country and available for sea warfare