cobalt blue vs aquamarine

cobalt blue and aquamarine both are nouns.

Word	Noun	Adjective	Verb	Adverb
cobalt blue	Yes	No	No	No
aquamarine	Yes	No	No	No

As nouns, cobalt blue and aquamarine are synonyms defined as:

Other synonyms of cobalt blue include aqua, greenish blue, peacock blue, turquoise.

cobalt blue (noun)	aquamarine (noun)
a shade of blue tinged with green	a shade of blue tinged with green
greenish-blue pigment consisting essentially of cobalt oxide and alumina	a transparent variety of beryl that is blue green in color