reddish brown vs sepia

reddish brown and sepia both are nouns.

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

As nouns, reddish brown and sepia are synonyms defined as:

Other synonyms of reddish brown include burnt sienna, mahogany, Venetian red.

reddish brown (noun)	sepia (noun)
a shade of brown with a tinge of red	a shade of brown with a tinge of red
	rich brown pigment prepared from the ink of cuttlefishes