Earn enough 'Fitcash' by playing the various balance games and your Fitpiggy will do a little dance and change colour.

Color	How to unlock
Bronze Fitpiggy	Accumulate 10 hours of training time.
Crystal Fitpiggy	Accumulate 120 hours of training time.
Gold Fitpiggy	Accumulate 40 hours of training time.
Silver Fitpiggy	Accumulate 20 hours of training time.