Another one of those 'easily fixed' issues, which if you're designing the front door of the world's most popular electronic device shouldn't have made it this far to begin with.
The first thing you do when designing something where the user can change the background, is try out a variety of backgrounds.
Update: I hear tell on the Twitters that for some people the text switches to black when they use white backgrounds; so you can assume this is a bug. That said, I imagine it won't fare well against a black/white checkered pattern.
Disclaimer: I understand iOS 7 is in beta. My point with these posts is that some of these are things are fundamentally misconceived. Apple is no slouch, I'm sure in time they'll fix these issues. But much of this stuff shouldn't have left the whiteboard if you ask me. Also, I believe in publicly discussing these issues so that we can all learn from them and educate each other.