deep brown vs brownness

deep brown and brownness both are nouns.

Word	Noun	Adjective	Verb	Adverb
deep brown	Yes	No	No	No
brownness	Yes	No	No	No

As nouns, brownness is a hypernym of deep brown; that is, brownness is a word with a broader meaning than deep brown:

Other hypernyms of deep brown include brown.

deep brown (noun)	brownness (noun)
a medium brown to dark-brown color	an orange of low brightness and saturation