Every species has three color variants which must be discovered through various means. Feeding a piñata certain items will change their color, sometimes they have to eat more than one item to change colors. For example, if you feed a Turnip to a Whirlm, it changes color to a purple Whirlm, but you have to feed a Daisy and a Bluebell to a Mousemallow for it to change to a white Mousemallow.
If you change the color of a piñata once you can't change it again. So to get all 3 of the variants you have to have 3 separate pinatas to change each to a different variant.
Every time you discover a new variant you will gain four petals of experience.
In addition to their color variants, some species are also able to evolve into a different species. For example, if you feed a Buttercup to a Sparrowmint it becomes a Candary. Another well-known example is a Horstachio turning into a Zumbug after eating one Blackberry and one Daisy, as seen on the Horstachio of a Different Color TV episode.