iOS 4.2 has added a “triple-click home button” feature with accessibility options, so now it’s possible to set white/black mode by going to “General Settings -> Accessibility -> Triple-click Home” and choosing the “White/Black” option. Once done, you can switch the iPhone to inverted colors at any time by hitting the home button three times in quick succession.
I still consider this a “hack”, as it turns your entire phone into inverted color mode. I would still prefer iBooks to have a true white text on black background like the Kindle and Stanza apps do.
One thing lacking from the updated iBooks app that’s now available for iPhones is the ability to read with white-on-black text. Black-on-white and black-on-sepia are your only native options.
A hackish way for getting white-on-black (my preference for reading in a dark room) is to go into the iPhone’s General Settings -> Accessibility and setting the “White on Black” switch to “ON”. Now iBooks is in white-on-black, but so iseverything else on your iPhone, and to make everything “normal” again when you’re done in iBooks, you have to go back into your general settings to turn white-on-black off. Kind of a pain, but it works, mostly.
Come on, Apple, make white-on-black a standard color choice in iBooks. (You know, like the Kindle app does. Just sayin’.)
(P.S. For those who might be wondering, some people with vision impairment are sensitive to light, which is why most accessibility settings in computers offer a white-on-black or inverted setting.)