What does Rainbow Series mean?
The “rainbow series” is a number of books and manuals with differently colored covers. One of the most common references to the rainbow series refers to a set of security manuals put out by the U.S. Department of Defense National Computer Security Council, where books had many different-colored and brightly colored covers.
Techopedia explains Rainbow Series
In addition to the NCSC rainbow series, which covered aspects of computer security and security protocol, other sets of books have also been called a “rainbow series.” For example, there is the series of books involved in documenting standard references for PostScript, a page description language developed in the 1970s, which included a red book, green book, blue book and white book.
The general idea is that a series of manuals developed with distinctive colored covers is referred to in shorthand by their colors, and the entire series is referred to as a rainbow or “crayola” series – even in the digital age, print manuals and instructions books can be critically important, and part of what someone might call a “programmer’s bible” or other handy reference.