sapphire vs cerulean

sapphire and cerulean both are nouns.

Word	Noun	Adjective	Verb	Adverb
sapphire	Yes	Yes	No	No
cerulean	Yes	Yes	No	No

As nouns, sapphire and cerulean are synonyms defined as:

Other synonyms of sapphire include azure, lazuline, sky-blue.

sapphire (noun)	cerulean (noun)
a light shade of blue	a light shade of blue
a transparent piece of sapphire that has been cut and polished and is valued as a precious gem
a precious transparent stone of rich blue corundum valued as a gemstone

sapphire (adjective)	cerulean (adjective)
of something having the color of a blue sapphire	of a deep somewhat purplish blue color similar to that of a clear October sky