: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}, {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.
-- The AI Hackers Dictionary