mahogany vs reddish brown

mahogany and reddish brown both are nouns.

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

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

Other synonyms of mahogany include burnt sienna, sepia, Venetian red.

mahogany (noun)	reddish brown (noun)
a shade of brown with a tinge of red	a shade of brown with a tinge of red
any of various tropical timber trees of the family Meliaceae especially the genus Swietinia valued for their hard yellowish- to reddish-brown wood that is readily worked and takes a high polish
wood of any of various mahogany trees; much used for cabinetwork and furniture