For this, you just need to change an outfit's colors. For most modes, this is not possible until you beat the main story. However, it is already unlocked in Gauntlet Mode.
So, on the Gauntlet Mode character select screen, choose someone, then hit X to view the models. Select one of them and hit X to go to the color edit screen. Make any change to any of the colors for the achievement to unlock.
Also to note, the colors for DLC outfits cannot be altered.