blue-green vs bluish green

blue-green is not a noun while bluish green is a noun.

Word	Noun	Adjective	Verb	Adverb
blue-green	No	Yes	No	No
bluish green	Yes	Yes	No	No

As adjectives, blue-green and bluish green are synonyms defined as:

Other synonyms of blue-green include teal.

blue-green (noun)	bluish green (noun)
	a blue-green color or pigment

blue-green (adjective)	bluish green (adjective)
of a bluish shade of green	of a bluish shade of green