be sailing under false colours
be sailing under false colors
To be operating under the guise of false pretenses, so as to deceive someone or to hide one's true nature or intentions. (An allusion to the identifying flags of a ship.) Tim thought he could just put on fancy clothes and rub elbows with the upper crust that Janet's family socialized with, but everyone at the party knew he was sailing under false colors. Lest you think I'm sailing under false colors, let me say straight away that I'm being paid to give a review of this product today.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
be sailing under false coloursBRITISH
If someone or something is sailing under false colours, they are deliberately deceiving people. Note: A ship's colours are its national flag. This report sails under false colours. It claims to be a fair and rigorous examination of the issue, but it is no such thing. Note: When pirate ships spotted a treasure ship, they often took down their own flag and raised the flag of a friendly nation, in order to get close enough to the ship to attack it.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012