I always think of a nice feature all reader programs should have: an option to reverse the output onscreen.
Normally our documents are black text over white background, mimicing the way we are used to in paper documents. PDF is a really nice format because we can have carefully laid out document in digital format.
But think about it: to read a book on screen is like staring at a bulb. It would be nice to read white texts over black background.
But one should not expect for a PDF to be produced this way (anyway, printed media should be black over white). This support must come from the reader program: just reverse the client area (page) where the text is rendered.
For a glimpse of the result, one can issue the following command under X:
xcalib -i -a
The whole X screen will be reversed. I'd like to see this implemented directly in acrobat reader, with a handy shortcut to switch back and forth quickly.
There is a preference to do exactly that - replace the document's foreground and background colors. You can find it under Edit->Preferences->Accessibility->Replace Document Colors. The foreground and background colors that one wishes to be used can be specified here.
By the time I've file this bug entry I did already seen this option, but were concerned about text written in other colors. What I missed that time was the "Only change the color of black text or line art" option.
Actually I am still concerned. Think about gray-almost-black-but-still-gray text. Over white background it will look nice. Over black background, since it isn't black text, well, I don't know how Acrobat Reader will behave.