racer vs black racer

racer and black racer both are nouns.

Word	Noun	Adjective	Verb	Adverb
racer	Yes	No	No	No
black racer	Yes	No	No	No

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

racer: slender fast-moving North American snakes
black racer: blackish racer of the eastern United States that grows to six feet

racer (noun)	black racer (noun)
an animal that races	blackish racer of the eastern United States that grows to six feet
slender fast-moving North American snakes
a fast car that competes in races
someone who drives racing cars at high speeds