blue air vs wild blue yonder

blue air and wild blue yonder both are nouns.

Word	Noun	Adjective	Verb	Adverb
blue air	Yes	No	No	No
wild blue yonder	Yes	No	No	No

As nouns, blue air and wild blue yonder are synonyms defined as:

Other synonyms of blue air include blue, blue sky.

blue air (noun)	wild blue yonder (noun)
the sky as viewed during daylight	the sky as viewed during daylight