oxford gray vs greyness

oxford gray and greyness both are nouns.

Word	Noun	Adjective	Verb	Adverb
oxford gray	Yes	No	No	No
greyness	Yes	No	No	No

As nouns, greyness is a hypernym of oxford gray; that is, greyness is a word with a broader meaning than oxford gray:

Other hypernyms of oxford gray include gray, grayness, grey.

oxford gray (noun)	greyness (noun)
a very dark grey color	a neutral achromatic color midway between white and black