clay vs red clay

clay and red clay both are nouns.

Word	Noun	Adjective	Verb	Adverb
clay	Yes	No	No	No
red clay	Yes	No	No	No

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

clay: a very fine-grained soil that is plastic when moist but hard when fired
red clay: clay whose redness results from iron oxide

clay (noun)	red clay (noun)
the dead body of a human being	clay whose redness results from iron oxide
a very fine-grained soil that is plastic when moist but hard when fired
water soaked soil; soft wet earth