[Pharo-users] inverting colors of athens(cairo)canvas

Is it possible to invert the colors of a Athens Canvas? After some digging I found paintMode and paintTransform; however the former doesn't support such method (maybe some combination of xor and over?); and the former is only for some specific colors. I also tried changing Color>>asAthensPaintOn: ^ (Color white - self) alpha: (self alpha) "invert the color" and while this works nicely for most cases, it is overriding a library and _doesn't_ work for bitmaps (for obvious reasons). So is there some way how to invert it? Effectively a mask over the canvas. (Doing it at Morphic level should also be a viable option, provided it is possible there). Thanks, Peter