The Jargon File (version 4.4.7, 29 Dec 2003):

rainbow series
 n.

    Any of several series of technical manuals distinguished by cover color.
    The original rainbow series was the NCSC security manuals (see Orange Book
    ). These are now available via the web. the term has also been commonly
    applied to the PostScript reference set. Which books are meant by ?the
    rainbow series? unqualified is thus dependent on one's local technical
    culture.


The Free On-line Dictionary of Computing (30 December 2018):

rainbow series

    Any of several series of technical manuals
   distinguished by cover colour.  The original rainbow series
   was the NCSC security manuals (see Orange Book, crayola
   books); the term has also been commonly applied to the
   PostScript reference set (see Red Book, Green Book, Blue
   Book, White Book).  Which books are meant by ""the" rainbow
   series" unqualified is thus dependent on one's local technical
   culture.

   [Jargon File]

   (1996-12-03)