In the SSB series, each character can change his/her outfit's color to advoid confusion if he/she is facing the same character they're using.
SSB
SSBM
The player can chose to control Popo or Nana and have the other Ice Climber follow you.
One of Mario's costumes makes him have Wario's (original) outfit.
One of Mewtwo's costumes makes him look light green. In the 2nd generation of Pokemon games and onward, this was Mewtwo's "shiny" color.
One of Peach's costumes makes her look like Daisy.
All of Kirby's and Yoshi's costumes are shown in their video games.
SSBB
Squirtle is the first character to have a comfirmed Alternate Costume (his shell becomes lightblue).
One of mario's costumes will be fire mario.