What is the origin of the phrase "to pass with flying colours"?

C
"colours" has generally meant identifying flags, especially on ships. Flying the flags, or colours on return from a war or a skirmish meant victory, while no flag flying denoted defeat. It was also used on land, as victory in battle was indicated by the hoisting of the company flag, which told both sides who had succeeded.

To 'pass with flying colours' comes from old naval traditions. Ships that returned from battle or a successful journey would fly their flags proudly to show victory. Over time, this idea turned into a metaphor-so now, when someone succeeds impressively, especially in a test or challenge, we say they 'passed with flying colours'. It's like saying they came through triumphantly.

https://en.m.wikipedia.org/wiki/With_flying_colours