There are several ways to change your pet's appearance. The most common is probably by painting it to change the color. You can also change the species or color of your pet with a magic potion. And, if you get access to the lab ray by collecting the map pieces, you can "zap" your pet, randomly changing its color, species, characteristics (such as speed, intelligence or defense strength) or even its gender. Sometimes a random event will change your pet. Recently (early 2007) many pets have known been randomly zapped to baby by a Bruce named Boochi. Magical plushies are another method. Play with one, and your pet will change to the style and species of the plushie. Once played with, the plushie will become a normal plushie.
more on each of these methods later...
For more information on each method, see
Chia Flour and Kacheek Flour will change your neopet into either a yellow Chia or blue Kacheek. Chia Flour is 35,000,000 NP and retired while Kacheek Flour is 22,000,000 NP and not retired.
Chias can change their appearance by eating a magical chia pop. When a Chia eats a Chia Pop, it will change to look like whatever fruit or vegetable is in the name of the Chia Pop. Non-magical chia pops have no known outcome whatsoever on the Chia's appearance. Only Usuls & Quiggles can be painted Usuki, and only Aishas can be the colour Alien (it is an extremely rare effect from the lab ray, so if a pet gets zapped Alien, it will automatically become an Aisha.) A few colors like clay and custard are available to very few pets, about 7-10.