steel gray vs iron blue

steel gray and iron blue both are nouns.

Word	Noun	Adjective	Verb	Adverb
steel gray	Yes	No	No	No
iron blue	Yes	No	No	No

As nouns, steel gray and iron blue are synonyms defined as:

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

steel gray (noun)	iron blue (noun)
slightly purplish or bluish dark grey	any of various blue pigments
	slightly purplish or bluish dark grey