Nothing beats the actual German wartime building specs...
From the Allegmeinen building regulations No. 31, edition March 1940
From the Allegmeinen building regulations No. 31, edition July 1944
In German, but I'm sure someone can translate better than Babelfish.
You can match it to the RAL colour card here...
http://www.themeter.net/ral_e.htm
It seems...shock horror...that...shock...Das Boot may be...shock...wrong... Yeah, yeah, I know, impossible, but still...