cobalt blue vs blueness

cobalt blue and blueness both are nouns.

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

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

cobalt blue: a shade of blue tinged with green
blueness: blue color or pigment; resembling the color of the clear sky in the daytime

Other hypernyms of cobalt blue include blue.

cobalt blue (noun)	blueness (noun)
a shade of blue tinged with green	blue color or pigment; resembling the color of the clear sky in the daytime
greenish-blue pigment consisting essentially of cobalt oxide and alumina