Bug 409508

Okular has a few nice accesibility options to let the user change the background color for the documents if these are really text documents, not just scanned images. This is almost a must if one uses to read for long times in dark environments and loves his retinas: you set the document's background in a comfortable semidark color and you are almost dome. But I say "almost" because the ideal would be to have an almost black background, but you can't because Okular doesn't permit to change the text color, so you would end with a very dark background and black text, which is illegible. So, finally you use the "minor evil", not the optimal solution.
Theres an option to invert the colors for all the document, but this includes the images, something rather annoying; the read is nice but then you see the images in negative and something creaks in your brain.

So, my suggestions are to add the option to change the text color, my favorite, since this would give the option of configuring the look very granularly and make happy evry user out there; or add the possibility of excluding the images in the «Invert colors» option.