This article is from the Computer Security Evaluation FAQ, by Trusted Product Evaluation Program TPEP@dockmaster.ncsc.mil.
The Trusted Computer System Evaluation Criteria (TCSEC) is a
collection of criteria used to grade or rate the security
offered by a computer system product. The TCSEC is sometimes
referred to as "the Orange Book" because of its orange cover.
The current version is dated 1985 (DOD 5200.28-STD, Library No.
S225,711) The TCSEC, its interpretations and guidelines all
have different color covers, and are sometimes known as the
"Rainbow Series" (see Section II, Question 11.) It is available at