I hope we don't have to have everything themed white, even as beautiful as it looks.
One of the reasons most manufacturers stick to black/dark themes is to save that ever-so-valuable battery life on the person's mobile device.
Everything's pretty much a wait-and-see now, with iOS 7, it seems. But I don't expect Apple would change it.
But...
iPhones are using LCD-Displays (Yeah, i know what's wrong with that sentence), doesn't matter what color they are displaying for power consumption.
AMOLEDs are the display type that has a higher power consumption when displaying pictures with lots of white or other colors, because when they are displaying blacks, those pixels are actually off, drawing no/less power.
Another reason is life expectancy of the pixels of AMOLED displays - those displays will live longer if the OS is using a black theme, while a white or even worse blue theme (blue pixels have the shortest lifetime) woild decrease the life of the display.
As many important Android smartphones had been using AMOLED displays, Google made sure that Android devices are using less power by simply changing the main color for the Holo theme to black. (They also had some design conventions concerning PenTile matrix displays).
The problem with this is - apart from technology deciding how the interface should look - black backgrounds lead to less legibility when outside AND AMOLED displays also don't have a brightness as high es the one the iPhone reaches (if you look at the full display, like surfing on a page with a white background - if you only have a single white spot on the display, with the rest black - they can reach a high brightness - but there's no real life use case for this).
So:
For an iPhone, it doesn't matter if the UI is white, grey, black, green or pink - the screen always draws the same power.
This is different with many Android phones.
