The Rainbow Pool
One of the great joys of Neopia is being able to customize the look of your Neopets and Petpets with magical paint brushes. Paint brushes can be found via Random Events, won in contests or games, or purchased in shops. If you want to change ONLY the color of you Neopet (not its species), then you need to put the paint brush in your inventory and go to the Rainbow Pool, at which point you can use the paint brush to paint your Neopet. Once you use a paint brush, it disappears forever, so use it wisely! Don't forget to make sure that your Neopet's species is available in the color you want to paint it.
Petpets can also be painted different colors using Petpet Paint Brushes, but instead of going to the Rainbow Pool, you have to visit the nearby Petpet Puddle. Petpetpets cannot be painted.
Below is a lost of all paint brushes currently available, as well as a list of the colors which are not available via any paint brush.
Current Paint Brushes
Retired Colors (Can be won at the Rainbow Fountain)
Lab Ray Only Colors
Lastly, here are some random notes about different colors. First off, Neopets can become "mutants" by visiting the Lab Ray or by drinking a Transmogrification Potion. Secondly, a Neopet may permanently turn RED if it's angry or BLUE if it's sad. Some Random Events can change your Neopet's color, such as Boochi (who can make your Neopet a baby). Then there are the Ice Boris of Terror Mountain... they were only available for a short period of time and cannot be created or made via any form of transformation.
Finally, Chias are very odd Neopets because they can turn into fruits and vegetables (much to the delight of their enemies, the Lupes of Neopia). Chias are available in these unique colors: