Invert Color Shader (without see-through)

Hello Community!

I'm wondering how it's possible to achieve a Shader that inverts an objects color that it touches. Something like in the following video https://www.youtube.com/watch?v=X1xR8xQvgJc

I already found this shader: http://forum.unity3d.com/threads/invert-colors-shader.205244/

the problem with this one is, that the object (e.g. an Cube) where the shader is applied to acts like a mirror and inverts everything you look at. I want the object with the shader to be invisible and is just inverting the color of the objects thats inside it.

My Intention is to get a similar result like in the image: http://www.androidshock.com/wp-content/uploads/2013/10/Paper-Sorcerer-1.jpg

regards Soulart