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]
Words nearby show one's true colors
show one's colors,
show one's face,
show one's hand,
show one's heels,
show one's teeth,
show one's true colors,
show pony,
show signs of,
show someone a good time,
show someone out,
show someone the door