Inverse colours are seen through its breath.

A mid-sized postcreated creature, full white except its skull is black with black teeth and two cystal-like transparent canine teeth on both side. Skull has no eye sockets, just some deeper parts. Neck is covered with big feathers and its tail is basically just big feathers. Its name is Reverse and only special thing about it is skill to invert colours.
Basically Reverse in harmless thing, it's a quite shy and flees easily. Its senses are not the best in the world, though, and it can be surprised by random bypasser. Then Reverse uses its peculiar attack, streaming breath of...something. If it hits to a living creature (and to its head/eyes), that certain creature starts seeing inverted colours. Usually it confuses enough and Reverse can flee freely. Effect doesn't last long, just a couple of days. (Note: the breath does not change colours concretely, it just makes living things see inverted colours.) Another taken strike of Reverse's breath in another time lasts longer, and multiple times make sight of colours inverted for good. After that, the breath has no effect anymore. ... Colours look inverted also when just looking through Reverse's breath. The breath itself is colourless, it can be seen because it looks inverted colours from the environment.

Colour pencils, liners, copics, white ink. ....Fail trees....