How to change keyboard background color in iOS?

For the dark background use:

mytextfield.keyboardAppearance = UIKeyboardAppearanceAlert;

Read to find more information about UITextInputTraits (use UIKeyboardAppearanceDark at iOS 7+).

To change it globally, you can use appearance proxy in AppDelegate... I've tested it in iOS 8, Swift:

UITextField.appearance().keyboardAppearance = UIKeyboardAppearance.dark