There is a nice guide at the following address. The article is titled "Kriegsmarine U-Boat Colors and Markings" by Dougie Martindale, but it gets into surface ships as well. I just did a search under the title of the article and it came right up.
Also, you could try the Lifecolors Kriegsmarine paints available at Pacific Front Hobbies online, the naval wing of Freetime Hobbies.
www.artitec.nl/downloads/instructions/uboat/uboat...
Bill