Given how iOS 7 was designed, it should be (relatively) easy to make this possible. Would it not be just assigning different colors? They do it pretty well with maps.
Also, I think Jony and Craig are more likely to listen to people than Steve and Scott were. Given that this wouldn't be too difficult of a feature to implement, creating a petition may actually do us good.
Edit: Here's a mockup I did a while ago. What I find very interesting is that all of those vibrant colors that it uses, Work just as well against white vs. black. I think that was probably intentional. The more I think about it, I'd be surprised if we don't see this by iOS 8 (but i'd rather 7.1).
Image