brown bread vs dark bread

brown bread and dark bread both are nouns.

Word	Noun	Adjective	Verb	Adverb
brown bread	Yes	No	No	No
dark bread	Yes	No	No	No

As nouns, brown bread and dark bread are synonyms defined as:

Other synonyms of brown bread include whole meal bread, whole wheat bread.

brown bread (noun)	dark bread (noun)
dark steamed bread made of cornmeal wheat and flour with molasses and soda and milk or water	bread made with whole wheat flour
bread made with whole wheat flour