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Problem:
I've got to read lot's of pdf and djvu ebooks. They're mostly black text on white background. And this is very irritating for the eyes. Adjusting paper color often doesn't work because many documents contain scanned images instead of text. And it often doesn't work even for documents containing text. Changing dark and light colors doesn't work well too, cause it draws embedded truecolor pictures with just 2 colors.
Solutions:
1) Adjusting brightness/contrast/gamma of the document the way it was done in WinDjview or STDU Viewer on windows. There should also be a button on a toolbar to quickswitch the mode of viewing between using color adjustments and turning them off.

2) Add option to adjust brightness/contrast/gamma to "special windows settings". So that users could apply such options to any windows. Saving color settings to profiles with ability to adjust shortcuts (something like ctrl+shift+1 for color profile #1, etc.) will ease switching modes.

3) recently I saw an extension for google chrome called Turn off the lights. It darkens the webpage when viewing video. As far as I understand it draws a transparent image over the page. You can adjust level of transparency and color of the image.
The problem mentioned here could be solved in a similar way, and it should not be very difficult (I'm not a programmer, so I don't really know).