Earlier quoted context omitted.
Are you reading black-on-white or white-on-black? Google recently updated the Android maps application so everything is white during the day, which really annoys me. black-on-white is kind of obnoxious and wastes battery unless you're in full sunlight. But of course it's shinier, and shiny always beats functional...
It's not just shinier: in general people find it somewhat easier to read, as these blog posts with references to research suggest[1][2]. I know the halation effect mentioned in the second post completely ruines white-on-black for me, in most incarnations. My Gnome terminal is white-on-black, but that only works with a sufficiently large monospace font and the fact that terminal data is, well, different from a novel o…
Furthermore, Both of those posts are from before the iPhone, so I'd bet they were done on a full-sized computer screen. If I turn my Motorola Droid up to full brightness at night and read Reddit, I might as well be staring at a flashlight. Even low brightness is too much, especially at that range.
With the reddit-is-fun app I vastly prefer white-on-black. Right now I'm typing this on a 25" monitor, with my face 4 feet from the screen, and it's black-on-white in a browser box. But that's desktop.
What we need is a broad-based study with various smartphones and smartphone fonts at multiple brightness levels. (both backlight and ambient) I doubt that black-on-white is a good idea on a 4" screen with low ambient light. (At least not when you're reliant on a backlight.) At best, I would bet different fonts work well with different color schemes, and black-on-white should be avoided on portable devices to save battery power.