HEY LUIGI, WHAT'S DA HOLDAAAAAAP!!!?
It's usually the green people. e.g. Green Donkey Kong, Green Bowser, Green Popo, Green (or Purple) Ganondorf, Green Pikachu, Green Pichu, Green Jigglypuff, Green Charizard, and so on. If pink is available, it's what I go against too (Craptain Failcon, Luigi, Wario).