I've been using the invert colors feature to she it at night especially for sites that have a white background. Makes it much easier to read. I set my home button to it so I can triple click to turn it on.
That is kind of a sucky solution if you are looking at any graphics on a website, or any graphics at all. I wonder why Apple couldn't integrate inverted colors like Microsoft has done for many years, where the graphics are preserved. It would be a neat solution. Although simply providing the option for a dark theme would be just as neat. My wife isn't a big fan of the white on off white theme when she's trying to sleep.