red fox vs silver fox

red fox and silver fox both are nouns.

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

As nouns, silver fox is a hyponym of red fox; that is, silver 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
silver fox: red fox in the color phase when its pelt is tipped with white

Other hyponyms of red fox include black fox.

red fox (noun)	silver 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 tipped with white
New World fox; often considered the same species as the Old World fox
weedy annual with spikes of silver-white flowers