The Invisible Costume is a retired costume from the March 2017 Account Upgrades. Putting this costume on certain marapets will make it have a unique coloration behind some sort of fog. Unlike the name should suggest, the pets clearly aren't... well, invisible. There was already an Invisible avatar and that has been changed to 'Blank' with a new solution. If you already had this avatar before, it has changed to 'Blank'. There is an Invisible Paint Brush at Neopets, and if you back up a bit, they look very similar.