Occasionally an ordinary cargo ship or tanker would have a camoflage paint scheme that was more elaborate than the usual overall gray color. This was most common on British merchantmen or on ships that were being used as auxiliaries. I included several camoflage paint schemes for the Empire Freighter and the CAM-ship.
http://files.filefront.com/CAM-Ship..../fileinfo.html
http://files.filefront.com/Improved_.../fileinfo.html
Photos from uboat.net.