Most of my springboard wallpapers are light in color at the top, making it hard to see the white text on the time. Is there any way to darken the status bar some?
Apple does not allow apps or anything else to modify the system. And this would be something that modifies the system.
This is a reason that people jailbreak their iPhones. If you want some sort of transparency or to modify things on your iPhone you will need to jailbreak.