Invert colors of the active window Sometimes I work in low light and I need to invert the color of specific windows to reduce my eye strain. This could be my pdf viewer to web pages for reference work. I know how to invert the entire screen: xcalib -invert -alter But I can't find any man pages, docs or posts how to invert _a single window only_. I did this before yet cannot find how. Bizarre! Searching the repos for other xorg tools I found xpdf, it has invert support but won't help for anything other than viewing pdf's. I don't use compositing so please don't suggest Compiz. I use Openbox WM. Thanks all. **Update** Instead of a general all-purpose tool to invert any window, I focused my search on how to invert colors for a Google Chrome tab instead. I found Color Bookmarklets, you drag them to the browser toolbar and hit them to change the page content to invert the colors (invert lightness).

If you are looking for a method universal for any window, then this must be made available by the window manager. Therefore I'm afraid any non-composite WM will not be able to do that on demand. So maybe you previously did this with Compiz?

A method of inverting colors regardless of WM is doing this per-application - as with `xpdf` that you mentioned. There are some applications that have such functionality, but usually you won't be able to invert the colors at run-time. For apps like `xpdf`, you can either have an alternative desktop menu entry (or icon) that runs the app with special parameters, or define those in your `.Xdefaults`. For `xpdf` note also the use of `paperColor`, `foreground` and `background` resources.