pistachio green vs greenness

pistachio green and greenness both are nouns.

Word	Noun	Adjective	Verb	Adverb
pistachio green	Yes	No	No	No
greenness	Yes	No	No	No

As nouns, greenness is a hypernym of pistachio green; that is, greenness is a word with a broader meaning than pistachio green:

pistachio green: A pale yellow-green colour, like that of the pistachio nut.
greenness: green color or pigment; resembling the color of growing grass

Other hypernyms of pistachio green include green, viridity.

pistachio green (noun)	greenness (noun)
A pale yellow-green colour, like that of the pistachio nut.	green color or pigment; resembling the color of growing grass
	the lush appearance of flourishing vegetation
	the state of not being ripe