Source : Free On-Line Dictionary of Computing

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)