Davy's grey vs iron blue

Davy's grey and iron blue both are nouns.

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

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

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

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