wild blue yonder vs blue air

wild blue yonder and blue air both are nouns.

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

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

Other synonyms of wild blue yonder include blue, blue sky.

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