Luftwaffe Aircraft Camouflage and Markings
German aircraft colors were methodically specified by the Reichsluftfahrt Ministerium (State Ministry for Aviation, but it sounds funnier in German). During the later years of the war, when Luftwaffe factories were under seige from the allied air offensive, the widespread dispersal and scarcity of resources rendered any efforts at standardization moot, so late war colors were subject to much greater variability than earlier in the war. Likewise, the far flung offensives of the German armed forces meant that the Luftwaffe was forced to fly and fight in a wide variety of climates, so locally-applied field camouflage was commonplace, and insured that enough variety existed in Luftwaffe coloration to keep model builders from repeating themselves for decades.
Thanks to the German propensity for documenting everything, a great wealth of information regarding Luftwaffe camouflage exists today, and can easily be found on the web. The magic keyword is "RLM". Some great reference sites are the IPMS Stockholm website, Hyperscale's Digital Color Charts and The Luftwaffe in Scale. Those of you interested in deciphering the unit codes on the fuselages of Luftwaffe aircraft will find a treasure trove of information at The Luftwaffe in Scale site, and some helpful hints at modelingmadness.com
For physical samples (which were used to divine the reasonably accurate approximations of Luftwaffe color seen here) I highly recommend Eagle Strike Publications "Luftwaffe Color Charts", whose color chips were reproduced from original archive specimens by one the Luftwaffe's wartime paint suppliers, Warnecke and Bohm.