/bu̇k tī-tᵊls/
There is a tradition in hackerdom of informally tagging important textbooks and standards documents with the dominant color of their covers or with some other conspicuous feature of the cover. Many of these are described in this lexicon under their own entries.
See Aluminum Book, Blue Book, Cinderella Book, Devil Book, Dragon Book, Green Book, Orange Book, Pink-Shirt Book, Purple Book, Red Book, Silver Book, White Book, Wizard Book, Yellow Book and Bible.