red fox vs black fox

red fox and black fox both are nouns.

Word	Noun	Adjective	Verb	Adverb
red fox	Yes	No	No	No
black fox	Yes	No	No	No

As nouns, black fox is a hyponym of red fox; that is, black fox is a word with a more specific, narrower meaning than red fox:

red fox: the common Old World fox; having reddish-brown fur; commonly considered a single circumpolar species
black fox: red fox in the color phase when its pelt is mostly black

Other hyponyms of red fox include silver fox.

red fox (noun)	black fox (noun)
the common Old World fox; having reddish-brown fur; commonly considered a single circumpolar species	red fox in the color phase when its pelt is mostly black
New World fox; often considered the same species as the Old World fox
weedy annual with spikes of silver-white flowers