title: Fade in/out whole view exept one subview
body: <p>I try to recreate an effect in the Path app : when you tap a photo/video all the views fade in except the one you just tapped which goes fullscreen.</p>
  
  <p>I wonder how such effect is done because if you change the alpha of your main view, all subviews are affected including the one you want to stay visible. If you do a for loop to change the alpha of all subviews exept the photo, the background will keep its colour.</p>
  
  <p>The only way I can think of is to do the for loop through all subviews and to set the background colour to black. But in my opinion it's not really clean code. </p>
  
  <p>What do you think?</p>