copper vs reddish brown

copper and reddish brown both are nouns.

Word	Noun	Adjective	Verb	Adverb
copper	Yes	No	Yes	No
reddish brown	Yes	No	No	No

As nouns, reddish brown is a hypernym of copper; that is, reddish brown is a word with a broader meaning than copper:

Other hypernyms of copper include burnt sienna, mahogany, sepia, Venetian red.

copper (noun)	reddish brown (noun)
any of various small butterflies of the family Lycaenidae having coppery wings	a shade of brown with a tinge of red
a reddish-brown color resembling the color of polished copper
uncomplimentary terms for a policeman
a copper penny
a ductile malleable reddish-brown corrosion-resistant diamagnetic metallic element; occurs in various minerals but is the only metal that occurs abundantly in large masses; used as an electrical and thermal conductor

copper (verb)	reddish brown (verb)
coat with a layer of copper