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.

jemanden in seinen wahren Farben zeigen, jemandes wahres Gesicht zeigen

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

:
The crisis really showed him in his true colors.
Die Krise zeigte ihn wirklich in seinen wahren Farben.
His actions eventually showed him in his true colors to everyone.
Seine Handlungen zeigten ihn schließlich in seinen wahren Farben allen.