Mirror Match

A Mirror Match refers to a match in which two players face off against each other using the same character.

Street Fighter
While mirror matches were not technically possible in the original Street Fighter due to there being only one playable character, the two-player mode would pit Ryu against Ken, who at the time shared the same exact moveset.

Street Fighter II series
With Street Fighter II came the true advent of Mirror Matches, making it possible for players to challenge each other with the same character. In the event a mirror match is set up, the second player's color palette changes automatically, to avoid confusion between the two characters.