Is it possible to change only one screen color ?

[XPcentric]

For example, when pressing Ctrl+Alt+Cmd +8, all the screen colors are inverted. What I need is to only change one color.

What I'm trying to do is to change the white background while reading in Skim, if I could make it similar to sepia tone in Kindle. Since the feature to change background is not available on Skim, and dont have such good skills to tweak it myself, maybe I find a way to change one screen color, in which case it will be useful with any application I use, inlcluding web browser.

thanks!