sky-blue vs sapphire

sky-blue and sapphire both are nouns.

Word	Noun	Adjective	Verb	Adverb
sky-blue	Yes	Yes	No	No
sapphire	Yes	Yes	No	No

As nouns, sky-blue and sapphire are synonyms defined as:

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

sky-blue (noun)	sapphire (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

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