The Rainbow Pool (RP) is located next to the Money Tree in Neopia Central. If you look at the map of Neopia, you can see a Rainbow leading from Neopia Central to Roo Island. That is the rainbow from the RP. If you can obtain a paintbrush (PB), you can paint your pets at the RP. Okay, let's say you have a Gnorbu that you want to paint Plushie. You can either win a Plushie PB or buy one. (You can also use the Rainbow Fountain, although you must earn a quest from the Fountain Faerie in order to use it.) Once you have a Plushie PB, go to the RP and on the front page, you will see a picture of your PB and your pets. Under the PB, you will see a drop-down list. Select the name of your Gnorbu and submit your decision. Your Gnorbu will appear painted Plushie. Some pets, when in certain colors, have exclusive customizable items that can be taken off or put on whenever you'd like.
Rainbow Pool

The Rainbow Pool in Neopia Central