steel gray vs steel grey

steel gray and steel grey both are nouns.

Word	Noun	Adjective	Verb	Adverb
steel gray	Yes	No	No	No
steel grey	Yes	No	No	No

As nouns, steel gray and steel grey are synonyms defined as:

Other synonyms of steel gray include Davy's gray, Davy's grey, iron blue.

steel gray (noun)	steel grey (noun)
slightly purplish or bluish dark grey	slightly purplish or bluish dark grey