see false colors.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
How to use under false colors in a sentence
Syrup Cocillana Compound is a nostrum sailing under false colors.
It would seem, he said, from what he could learn, that Tillotson's honorable opponent was sailing under false colors.The Gay Cockade | Temple Bailey
To be constantly forced to move under false colors was a bitter thing for Ezra.The Young Continentals at Bunker Hill | John T. McIntyre
It is clear that the women calling themselves Mowbrays have had the audacity to present themselves here under false colors.The Princess Virginia | C. N. Williamson
That fellow is a Custom House inspector all right, but he's sailing under false colors.The Bradys and the Girl Smuggler | Francis W. Doughty