这个自定义的uiAlertView怎么样?

这是我制定的准则……

  - (void)willPresentAlertView:(UIAlertView *)alertView
    {
        [[[alertView subviews] objectAtIndex:2] setBackgroundColor:[UIColor colorWithRed:0.5 green:0.0f blue:0.0f alpha:1.0f]];
    }

    - (void) presentSheet
    {
        UIAlertView *baseAlert = [[UIAlertView alloc] 
                                  initWithTitle:@"Alert" message:@"This alert allows the user to choose between a 'safe' and a 'deadly' choice, indicated by button color.\n\n\n\n" 
                                  delegate:self cancelButtonTitle:nil
                                  otherButtonTitles:@"Deadly!", @"Safe", nil];
UITextField *txtFld = [[UITextField alloc] initWithFrame:CGRectMake(60,10,240,31)];
[txtFld setDelegate:self];
[txtFld setBackgroundColor:[UIColor clearColor]];
[baseAlert addSubView:txtFld];
[txtFld release];
        [baseAlert show];
    }

我的问题是,是否允许它改变苹果提供的uicontrols的基本外观和感觉,因为我看不出苹果不允许这种定制的任何理由。