cobalt blue vs greenish blue

cobalt blue and greenish blue both are nouns.

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

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

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

cobalt blue (noun)	greenish 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