I and several others (perhaps thousands) have a small problem. We have purchased and received an HP LP2475w LCD monitor with a slight defect. Some of these otherwise lovely monitors have a slight shifting color cast, reddish on the right side and greenish on the left. I was wondering if the compositing features of kwin could be used to fix this problem by presenting a transparent layer of some sort (window, desktop, whatever) with an inverse color cast to cancel out the one in the display. Never mind, for now, how such a thing might be generated, but is it possible to do? would it work?

You may find System Settings > Display > Gamma to be of help.

Thank you bcooksley for your response. I have tried all of those types of controls including monitor profiles to no avail, as would be expected. Perhaps I didn't make myself clear - the color cast varies from location to location on the screen. All of the above adjustments affect the screen in the same way, indepenent of location. What I need is a mechanism that would apply a correction that varies spatially. Imagine, to simplify things greatly, taking a photograph of the monitor displaying a neutral gray field, taking the negative of that image (if that's actually the correct transform), and compositing it as a transparent layer to apply the correction. The question is, can I use kwin to do this? Can I use kwin to display some arbitrary image and set it's transparency?

KWin itself cannot do that, at least not currently. Given that a plugin to it can perform drawing anywhere though, it may be possible to use KWin to paint a mask over the entire screen which would invert the effect.