dark-brown vs brownish

dark-brown and brownish both are adjectives.

Word	Noun	Adjective	Verb	Adverb
dark-brown	No	Yes	No	No
brownish	No	Yes	No	No

As adjectives, dark-brown and brownish are synonyms defined as:

Other synonyms of dark-brown include brown, chocolate-brown.

dark-brown (adjective)	brownish (adjective)
of a color similar to that of wood or earth	of a color similar to that of wood or earth