white book vs written report

white book and written report both are nouns.

Word	Noun	Adjective	Verb	Adverb
white book	Yes	No	No	No
written report	Yes	No	No	No

As nouns, written report is a hypernym of white book; that is, written report is a word with a broader meaning than white book:

white book: a government report; bound in white
written report: a written document describing the findings of some individual or group

Other hypernyms of white book include report, study.

white book (noun)	written report (noun)
a government report; bound in white	a written document describing the findings of some individual or group