Correct Answer: Real character.

Solution : The correct choice is the third option .

The idiom true colours refer to someone's real or genuine character, intentions, or personality traits, especially when they are revealed or shown, often in contrast to how they initially presented themselves.

Black and white is also an idiom, but it signifies something that is straightforward, clear, or unambiguous.

So, the most appropriate meaning of this idiom is to reveal someone's real or genuine nature or character.