True colours

To show one's true colours is to reveal what one is really like, to uncover one's real character or intentions, good or bad. It derives from the days of sail when ships used to identify themselves to other ships by means of 'colours' or flags. Pirates, or nations at war, often used to fly false colours or flags to deceive ships that they were about to attack. Nations at war would generally remove their false colours and reveal their true colours when about to engage in battle. The expression is first cited in its figurative sense in Thomas Becon’s A Fruitful Treatise of Fasting in 1551, in which Satan 'Setteth forth him selfe in his true colours'. Shakespeare used the expression later, in Henry IV Pt II Act II scene II: 'How might we see Falstaffe bestow himself tonight in his true colours'.