The Purple''''''Book is the BlueBook (''Smalltalk 80: The Language and Its Implementation'' by AdeleGoldberg and David Robson. ISBN 0-201-11371-6) without Part IV. Part IV is the implementation chapter, which is now freely available on the web. Somewhere.

(Also the Purple Book is the 3rd edition of Unix System Administration Handbook, the Red Book being the 2nd edition).

See SmalltalkTheLanguageAndItsImplementation