I’ve seen this SO question here: Can I tint (black) a UIKeyboard? If so, how?, where the top answer suggests that you can hack around but doing so may get your app rejected by Apple. This must not be true, as I’ve seen other iPhone applications (a major one being Clear) that have a black UIKeyboard. How is it done?
Here’s a screenshot of Clear for reference:

Try this out
or just adding
setKeyboardAppearance:UIKeyboardAppearanceAlertappropriately depending on how you have this set up!