show one's colors
show (one's) (true) colors
To reveal what one truly believes, thinks, or wants; to act in accordance with one's real personality, temperament, or disposition. Dave said all along that he only wanted this deal because it was in the company's best interest, but he showed his true colors once he realized that he wouldn't get any special commission for his efforts. It's only in times of crisis that your friends will really show their colors.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
show one's colors
see under false colors; also show one's true colors.
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.