greenish blue vs aquamarine

greenish blue and aquamarine both are nouns.

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

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

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

greenish blue (noun)	aquamarine (noun)
a shade of blue tinged with green	a shade of blue tinged with green
	a transparent variety of beryl that is blue green in color