powdery-blue vs powder blue

powdery-blue is not a noun while powder blue is a noun.

Word	Noun	Adjective	Verb	Adverb
powdery-blue	No	Yes	No	No
powder blue	Yes	Yes	No	No

As adjectives, powdery-blue and powder blue are synonyms defined as:

powdery-blue and powder blue: of a moderate to pale blue or purplish blue

powdery-blue (noun)	powder blue (noun)
	a pale blue color with grey in it

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