Change the keyboard "Done" button color to match the rest of your app! This is a total hack though and is likely to get flagged during app review. If so, try obfuscating =)

changeKeyboardDoneColor.swift

class Utilities {
  class func subviewsOfView(view: UIView, withType type: String) -> [UIView]
  {
    let prefix = "<\(type)"
    var subviewArray = view.subviews.flatMap { subview in subviewsOfView(subview, withType: type) }

    if view.description.hasPrefix(prefix) {
      subviewArray.append(view)
    }
    
    return subviewArray
  }
}

private func changeDoneButtonColorWhenKeyboardShows()
{
  NSNotificationCenter.defaultCenter().addObserverForName(UIKeyboardWillShowNotification, object: nil, queue: nil) { (notification) -> Void in
    self.changeKeyboardDoneKeyColor()
  }
}

private func changeKeyboardDoneKeyColor()
{
  let (keyboard, keys) = getKeyboardAndKeys()
  
  for key in keys {
    if keyIsOnBottomRightEdge(key, keyboardView: keyboard) {
      let newButton = newDoneButtonWithOld(key)
      keyboard.addSubview(newButton)
    }
  }
}

private func getKeyboardAndKeys() -> (keyboard: UIView, keys: [UIView])!
{
  for keyboardWindow in UIApplication.sharedApplication().windows {
    for view in keyboardWindow.subviews {
      for keyboard in Utilities.subviewsOfView(view, withType: "UIKBKeyplaneView") {
        let keys = Utilities.subviewsOfView(keyboard, withType: "UIKBKeyView")
        return (keyboard, keys)
      }
    }
  }
  
  return nil
}

private func keyIsOnBottomRightEdge(key: UIView, keyboardView: UIView) -> Bool
{
  let margin: CGFloat = 5
  let onRightEdge = key.frame.origin.x + key.frame.width + margin > keyboardView.frame.width
  let onBottom = key.frame.origin.y + key.frame.height + margin > keyboardView.frame.height
  
  return onRightEdge && onBottom
}

private func newDoneButtonWithOld(oldButton: UIView) -> UIButton
{
  let oldFrame = oldButton.frame
  let newFrame = CGRect(x: oldFrame.origin.x + 2,
                        y: oldFrame.origin.y + 1,
                        width: oldFrame.size.width - 4,
                        height: oldFrame.size.height - 4)
  
  let newButton = UIButton(frame: newFrame)
  newButton.backgroundColor = .secondaryColor
  newButton.layer.cornerRadius = 4;
  newButton.setTitle("Done", forState: .Normal)
  newButton.addTarget(self.searchBar, action: "resignFirstResponder", forControlEvents: .TouchUpInside)
  
  return newButton
}

Nice hack, but I'm not entirely convinced that this would get through review because you are fundamentally ignoring Apple's HIG on their own elements. Alternatively, you could probably write your own keyboard (new in iOS 8) to get past this restriction. I'd be interested to see if this got through review.

Sorry, didn't realize people would find this organically. When I posted this on FB I mentioned that this is likely to get flagged during review. I'll update the description

It is findable organically 😁