show your true colors definition
This page is about the idiom show your true colours | show your true colors. Meaning: You show your true colours if you show what you're really like, or you reveal your true character. For example: Bob always acts like he's a strong, brave guy, but when the hurricane hit he showed his true colors. He was too scared to go check on old Mrs Flowers, our next-door neighbour.
Showing Our True Colors is a book by Mary Miscisin. It means being your real self, as opposed to posing as someone or something you're not. I don't think the word would apply to your Spanish teacher. A person who exposes himself as a thief, would be someone who shows his true colors..... John McCain showed his true colors when he refused to jump the line in getting out of POW camp.