powder blue vs blueness

powder blue and blueness both are nouns.

Word	Noun	Adjective	Verb	Adverb
powder blue	Yes	Yes	No	No
blueness	Yes	No	No	No

As nouns, blueness is a hypernym of powder blue; that is, blueness is a word with a broader meaning than powder blue:

powder blue: a pale blue color with grey in it
blueness: blue color or pigment; resembling the color of the clear sky in the daytime

Other hypernyms of powder blue include blue.

powder blue (noun)	blueness (noun)
a pale blue color with grey in it	blue color or pigment; resembling the color of the clear sky in the daytime

powder blue (adjective)	blueness (adjective)
of a moderate to pale blue or purplish blue