As I was reading a magazine on the bus today I was thinking about what's easiest to read. I noticed the black-on-white text was easier to read than white-on-black, which I suppose is because blurring it damages the letter shapes less. It basically just reduces its contrast. But white-on-black is dimmer, and dimmer screens are less painful to look at. It occurred to me that the optimum is probably something like black on grey, but with white outlines around the letters. Have you seen anybody do that?