redness vs deep red

redness and deep red both are nouns.

Word	Noun	Adjective	Verb	Adverb
redness	Yes	No	No	No
deep red	Yes	No	No	No

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

redness: red color or pigment; the chromatic color resembling the hue of blood
deep red: a deep and vivid red color

redness (noun)	deep red (noun)
red color or pigment; the chromatic color resembling the hue of blood	a deep and vivid red color
a response of body tissues to injury or irritation; characterized by pain and swelling and redness and heat