aqua vs greenish blue

aqua and greenish blue both are nouns.

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

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

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

aqua (noun)	greenish blue (noun)
a shade of blue tinged with green	a shade of blue tinged with green