With Kwin it is possible to invert the screen colors.
So I was wondering is it also possible to do this per window (/application), ie. as a Kwin window rule?

I already looked in the window rule dialog (there is no option for it), but that my only be GUI specific and it is possible to add this option by editing the config file?

The ability to do this per window requires OpenGL compositing (afair GL2.0) and bears a significant overhead compared to the screen inversion.

The inversion effect is shortcut triggered, the core (thus the rules) can not be directly used for this.

---
A rather generic way to invoke the rules here could be a rule that sets random window properties (and the effect would have to interpret them). Notice that such is NOT implemented atm.