iOS7 Keyboard Return/Done/Search tint colour

You can not change button tint color but you can set keyboard Tint color by using UIKeyboardAppearance

Example: yourTextField.keyboardAppearance = UIKeyboardAppearanceDark;

Here is a very nice document provided by Apple, take a look here:

Managing the Keyboard

With a little hack maybe you can achieve the effect you are looking for. But it might not be able to pass the app review.

-(NSArray*)subviewsOfView:(UIView*)view withType:(NSString*)type{
    NSString *prefix = [NSString stringWithFormat:@"<%@",type];
    NSMutableArray *subviewArray = [NSMutableArray array];
    for (UIView *subview in view.subviews) {
        NSArray *tempArray = [self subviewsOfView:subview withType:type];
        for (UIView *view in tempArray) {
            [subviewArray addObject:view];
        }
    }
    if ([[view description]hasPrefix:prefix]) {
        [subviewArray addObject:view];
    }
    return [NSArray arrayWithArray:subviewArray];
}

-(void)addColorToUIKeyboardButton{
    for (UIWindow *keyboardWindow in [[UIApplication sharedApplication] windows]) {
        for (UIView *keyboard in [keyboardWindow subviews]) {
            for (UIView *view in [self subviewsOfView:keyboard withType:@"UIKBKeyplaneView"]) {
                UIView *newView = [[UIView alloc] initWithFrame:[(UIView *)[[self subviewsOfView:keyboard withType:@"UIKBKeyView"] lastObject] frame]];
                newView.frame = CGRectMake(newView.frame.origin.x + 2, newView.frame.origin.y + 1, newView.frame.size.width - 4, newView.frame.size.height -3);
                [newView setBackgroundColor:[UIColor greenColor]];
                newView.layer.cornerRadius = 4;
                [view insertSubview:newView belowSubview:((UIView *)[[self subviewsOfView:keyboard withType:@"UIKBKeyView"] lastObject])];

            }
        }
    }
}

The app I used to decode the view hierarchy was : http://revealapp.com/

The end result is like this: