hi, I'm new here, what the best pet and how to get potions to paint them?

There is no "best" pet, you can just go here and see which one you like best, and create one. You can buy potions from other users (shop search, trades), find one in a random event, participate in the potion lottery (games section), restock one from the Apolyptic Apothecary (shop), or use the pet zapper to change it into a random colour.

this is a good source to find what the different pets and colors look like :)

Welcome to the site. Unlike other pet sites, pets here have no particular value since trading is not allowed. Therefore there is no "best" pet per say. However some potions are more expensive than others. Some colors are known as colorfills which just changes the colors while others change the poses of the species and add details that differ from the standard position.