red ash vs green ash

red ash and green ash both are nouns.

Word	Noun	Adjective	Verb	Adverb
red ash	Yes	No	No	No
green ash	Yes	No	No	No

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

red ash: smallish American tree with velvety branchlets and lower leaf surfaces
green ash: a variety of red ash having glossy branchlets and lower leaf surfaces

Other hyponyms of red ash include Fraxinus pennsylvanica subintegerrima.

red ash (noun)	green ash (noun)
smallish American tree with velvety branchlets and lower leaf surfaces	a variety of red ash having glossy branchlets and lower leaf surfaces