pale yellow vs yellowness

pale yellow and yellowness both are nouns.

Word	Noun	Adjective	Verb	Adverb
pale yellow	Yes	No	No	No
yellowness	Yes	No	No	No

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

pale yellow: a variable yellow tint; dull yellow, often diluted with white
yellowness: yellow color or pigment; the chromatic color resembling the hue of sunflowers or ripe lemons

Other hypernyms of pale yellow include yellow.

pale yellow (noun)	yellowness (noun)
a variable yellow tint; dull yellow, often diluted with white	yellow color or pigment; the chromatic color resembling the hue of sunflowers or ripe lemons