Complete any of the following tasks in any order to earn a star and change the color of your trainer card, as indicated below: Defeat the Elite Four; win all of the Master Rank Contests, complete the Underground Flag mini-game with friends, capture 482 different Pokemon; or win 100 times in a row at the Battle Tower.

Blue Trainer Card (one star)
Bronze Trainer Card (two stars)
Silver Trainer Card (three stars)
Gold Trainer Card (four stars)
Black Trainer Card (five stars)