idiom
show one's true colors
揭示一个人的真实性格或感情,通常是在隐藏之后
Meaning
to reveal one's true character or feelings, often after a period of hiding them
Example
He finally **showed his true colors** when he volunteered at the charity event.
他在慈善活动中做志愿者时终于展现了他的真实面目。