redness vs spectral colour

redness and spectral colour both are nouns.

Word	Noun	Adjective	Verb	Adverb
redness	Yes	No	No	No
spectral colour	Yes	No	No	No

As nouns, spectral colour is a hypernym of redness; that is, spectral colour is a word with a broader meaning than redness:

redness: red color or pigment; the chromatic color resembling the hue of blood
spectral colour: a color that has hue

Other hypernyms of redness include chromatic color, chromatic colour, spectral color.

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