When the U.S. government writes the standards, and then becomes itself one of the largest customers for equipment that meets requirements defined by those standards, those standards become important very quickly. Add to this the fact that once the government overcomes its own bureaucratic forces to the point it actually accomplishes something, the corollary is that the work stays in force for a long time.
Such is the case of the Orange Book. Different organizations required different levels of security, and because security professionals needed a metric to gauge if a computer system was secure enough for the intended purpose, the government developed the Trusted Computer System Evaluation Criteria (TCSEC) and published them in a book that had an orange cover, hence the nickname “Orange Book.” The Orange Book was part of a family of publications on security with different colored covers called the Rainbow Book series. See the sidebar "Somewhere Over the Rainbow.”