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

1.
iemand in zijn ware aard laten zien, iemands ware gezicht tonen
to reveal someone's true character, especially if it is negative or unpleasant
:
•
The crisis really showed him in his true colors.
De crisis liet hem echt in zijn ware aard zien.
•
His actions eventually showed him in his true colors to everyone.
Zijn acties toonden hem uiteindelijk in zijn ware aard aan iedereen.