show one's true colors

show (one's) (true) colors

To reveal what one really 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.
See also: color, show

show one's true colors

Reveal oneself as one really is, as in We always thought he was completely honest, but he showed his true colors when he tried to use a stolen credit card . This expression alludes to the antonym, false colors, that is, sailing under a flag other than one's own. [Late 1700s]
See also: color, show, true

show one's true colors, to

To reveal oneself frankly; to admit one’s genuine opinions or character. This term, the converse of sail under false colors, similarly alludes to the practice of deceiving the enemy by flying a friendly flag. However, it also was applied to cosmetics used to conceal or enhance a complexion. Thus Thomas Dekker wrote (A Description of a Lady by Her Lover, ca. 1632), “The reason why fond women love to buy Adulterate complexion: here ’tis read,—False colours last after the true be dead.” The metaphor was used for one’s genuine character by numerous writers, Dickens among them: “He didn’t venture to come out in his true colours” (The Old Curiosity Shop, 1840).
See also: show, true
References in periodicals archive ?
Show one's true colors: From men-of-war that would approach an enemy ship while flying a friendly flag, then hoist their real flag immediately before opening fire.