To pass with flying colours
We usually use “to pass with flying colours” in conjunction with some type of test or exam to express the idea that the candidate has achieved high marks.
“ My son passed his exam with flying colours”. “ Oh really, that’s wonderful!”
But where does this phrase come from? Like other expressions still in common use today, this has its origins in nautical history and refers to the colourful flags flying from a masthead of a ship. In the past, before the use of the widespread communication channels of today, a ship’s appearance was the key to how they had fared on their voyage. If a ship had been defeated in battle, flags were not flown. But when a ship returned to port victorious from a mission, all their flags would be on display to show their achievement and to communicate this from afar, before the ship docked.
To show your true colours
In a similar way, “to show your true colours” also has its roots in naval history. Sometimes pirate ships would use the tactic of a friendly flag in order to deceive their prey and gain proximity. Once they had secured access to the ship, the pirate flag would be shown and they would attack in search of treasure. Of course, nowadays we use this expression to denote that someone has shown their real (usually unpleasant) feelings or personality after a period of initial friendliness.