blue green vs cyan

blue green and cyan both are nouns.

Word	Noun	Adjective	Verb	Adverb
blue green	Yes	No	No	No
cyan	Yes	Yes	No	No

As nouns, cyan is a hyponym of blue green; that is, cyan is a word with a more specific, narrower meaning than blue green:

blue green (noun)	cyan (noun)
a blue-green color or pigment	a primary subtractive color for light; has a blue-green color

blue green (adjective)	cyan (adjective)
	of the blue-green color that is a primary subtractive color of light