This page lists all the pet colours which have appeared on the servers, but have never been available as painting options in the Rainbow Pool. With the switch to the Customisation system, they are unlikely to be released, though some may be redrawn into the new style with few changes, such as the Speckled pets here. Stone and Glass pets are no longer available as colour options - they were released at one point, but all Glass pets became Tyrannian, and all Stone pets became Island.
This is a fairly comprehensive guide to unreleased colours, but if you have any images we're missing, email me and let me know.
Pet names in bold have since been released post-Customisation; click an image to be taken to the released pet's page. Some of these are similar to the original, such as the Rainbow Xweetok, while others are very different, such as the Faerie Hissi.