copper color vs burnt sienna

copper color and burnt sienna both are nouns.

Word	Noun	Adjective	Verb	Adverb
copper color	Yes	No	No	No
burnt sienna	Yes	No	No	No

As nouns, burnt sienna is a hypernym of copper color; that is, burnt sienna is a word with a broader meaning than copper color:

Other hypernyms of copper color include mahogany, reddish brown, sepia, Venetian red.

copper color (noun)	burnt sienna (noun)
a reddish-brown color resembling the color of polished copper	a shade of brown with a tinge of red
	a reddish-brown pigment produced by roasting sienna