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Related to false colours: sail under false colours
1. (Military) a flag to which one is not entitled, flown esp in order to deceive: the ship was sailing under false colours.
2. an assumed or misleading name or guise: to trade under false colours.
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014