cobalt blue vs aqua

cobalt blue and aqua both are nouns.

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

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

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

cobalt blue (noun)	aqua (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