Davy's gray vs iron blue

Davy's gray and iron blue both are nouns.

Word	Noun	Adjective	Verb	Adverb
Davy's gray	Yes	No	No	No
iron blue	Yes	No	No	No

As nouns, Davy's gray and iron blue are synonyms defined as:

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

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