red-brown vs reddish-brown

red-brown and reddish-brown both are adjectives.

Word	Noun	Adjective	Verb	Adverb
red-brown	No	Yes	No	No
reddish-brown	No	Yes	No	No

As adjectives, red-brown and reddish-brown are synonyms defined as:

Other synonyms of red-brown include mahogany-red.

red-brown (adjective)	reddish-brown (adjective)
of brown tinged with red	of brown tinged with red