Transparent Background Modal View

In the presenting View Controller add the following code if you want to support iOS7.

//	For iOS modal presentation style must be set on presenting view controller.
	if ([UIDevice currentDevice].systemVersion.integerValue >= 7)
		[self setModalPresentationStyle:UIModalPresentationCurrentContext];
		
	[self presentViewController:seeThroughViewController animated:YES completion:nil]; 

In the modal View Controller code add the following code

//	Allows the presenting View Controller to be seen through the modal view controller
[self setModalPresentationStyle:UIModalPresentationCustom];

출처 : http://b2cloud.com.au/how-to-guides/invisible-background-modal-view/