false colors

plural noun

1. the flag of a country other than one's own, especially when used deceptively.

   sailing under false colors.

2. false or deceptive actions or statements; misrepresentation.

Word History and Origins

Origin of false colors¹

1565–75, for literal sense

Idioms and Phrases

Pretense, misrepresentation, or hypocrisy; deceptive statements or actions. For example, She's sailing under false colors—she claims to be a Republican, but endorses Democratic legislation. This term alludes to the practice of pirate ships sailing under false colors —that is, running a particular flag specifically to lure another vessel close enough to be captured. [Late 1600s]