One reason it may be easier for your nephew to read white text on a black background is that all of his other gadgets are backlit (including the iPhone, which may be one reason you can change the background on the iPhone and not on the Kindle). The Kindle is not backlit -- it is just like reading text on regular paper. I guess my question would be, does he get regular books -- on paper -- that are black with white text? Doubtful, so it will be just as easy for him to read text on a Kindle as it would be for him to read a regular dead-tree book. Except he'll be able to increase the font size on a Kindle!