That's the thing - you can't see what's behind - take a look at the shot here: http://www.apple.com/ios/ios7/

If you look at control center - the flashlight glows green and the camera red. Why? Because some arbitrary icon that you can't even make out is that color behind it. I find that really odd.

Even if you could actually make out what's behind the layer, I don't see the utility (and I'd argue it's even more distracting).