(one's) true colours
One's true or honest beliefs, thoughts, convictions, biases, desires, etc.; one's real personality, character, or disposition. Primarily heard in UK. Dave said all along that he only wanted this deal because it was in the company's best interest, but he showed his true colours once he realised that he wouldn't get any special commission for his efforts. You will really see your friends' true colours when you call upon them in a time of crisis.