What are white papers, blue books and black books! Please explain in detail.

The cover is white, and it is called a white paper, such as the Statement on US-China Relations published by the United States in August 1949. The cover is blue, called blue book (such as Britain); The red one is called the little red book (such as Spain); Use yellow, called yellow book (such as France); Use green, called green book (such as Italy) and so on.