[UIView beginAnimations:@"Animate" context:nil];
[UIView setAnimationDuration:0.75];
[UIView setAnimationCurve:UIViewAnimationCurveEaseOut];
[UIView setAnimationTransition:UIViewAnimationTransitionCurlDown forView:self.view cache:YES];
[aViewController viewWillDisappear:YES];
[bViewController viewWillAppear:YES];
[aViewController.view removeFromSuperview];
[self.view addSubview:bViewController.view];
[aViewController viewDidDisappear:YES];
[bViewController viewDidAppear:YES];
[UIView commitAnimations];
当页面向下或向上时，我们可以看到第一页的背面。问题是，我想改变页面背面的颜色。我该如何处理？