UIViewAnimationTransitionCurDown\Up

Question

[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];

When the page down or up,We can see the back of the first page.The problem is,I want to change the color of the backside of the page. How can I deal with it?