greenish blue vs cobalt blue

greenish blue and cobalt blue both are nouns.

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

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

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

greenish blue (noun)	cobalt blue (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