yellowness vs spectral colour

yellowness and spectral colour both are nouns.

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

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

yellowness: yellow color or pigment; the chromatic color resembling the hue of sunflowers or ripe lemons
spectral colour: a color that has hue

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

yellowness (noun)	spectral colour (noun)
yellow color or pigment; the chromatic color resembling the hue of sunflowers or ripe lemons	a color that has hue