This is create 10 DIFFERENT characters in customize. And even then this is costume changes.
Go into customize and choose to change characters, choose 10 different characters, go to any of the color sets and change one color, backing out (make sure to save your changes, I believe that's required) and then do the same thing to 9 DIFFERENT characters. I stress that because each character has 5 different colors, changing all 5 only counts for a single character, not 5 different characters.
This should take a player less than 3 minutes.