show someone in their true colors

US /ʃoʊ ˈsʌm.wʌn ɪn ðer truː ˈkʌl.ərz/
UK /ʃoʊ ˈsʌm.wʌn ɪn ðer truː ˈkʌl.ərz/
"show someone in their true colors" picture
1.

讓某人露出真面目, 揭示某人的真實本性

to reveal someone's true character, especially if it is negative or unpleasant

:
The crisis really showed him in his true colors.
這場危機真的讓他露出了真面目
His actions eventually showed him in his true colors to everyone.
他的行為最終讓大家看清了他的真面目