Official Description: Every time your pet changes to a new color and/or species it will be added to it's Transformation Collection. The more of these you gain, the more prizes the Rainbow Fairy will reward you. You can also complete Drew quests to change your pet to a previous species or color. There are many Pet Dailies that can change your pet's colour or species. Here are all of the Pet Colours your pet can transform into.
There are many different items on the site that will increase your pet's transformation collection. Using an Enchanted Plushie or Potion will change your pet to a specific species and colour. A Costume will change your pet to a specific colour and a Fake Costume will only add the specific colour transformation to your pet's collection, without changing the pet's colour.
There are Enchanted Dips for every species of pet. You can use these on a matching species of pet and it will change your pet to a new, random colour. There is also an Essence for every species of pet and they will change your pet to a random colour of each species.
Additional Comments: The Portal is another method of changing your pet's color, but sometimes it may receive a stat change instead or nothing will happen. In addition to that there are other ways to change your pet's color. One of them is by using a Colour Concoction (the Illegal Concoctions Shop, however, is frequented by buyers; on top of this, your pet may go to Prison if caught using it).