Payne's gray vs Payne's grey

Payne's gray and Payne's grey both are nouns.

Word	Noun	Adjective	Verb	Adverb
Payne's gray	Yes	No	No	No
Payne's grey	Yes	No	No	No

As nouns, Payne's gray and Payne's grey are synonyms defined as:

Payne's gray and Payne's grey: any pigment that produces a greyish to dark greyish blue

Payne's gray (noun)	Payne's grey (noun)
any pigment that produces a greyish to dark greyish blue	any pigment that produces a greyish to dark greyish blue