title: How to add a semi-transparent shade over elements in WPF?
body: <p>I would like to add a semi-transparent colour over the contents of a WPF window (to indicate the state of the window). Currently I am using a UserControl that fills the Window, and I change the Background colour and Visibility as required.</p>
  
  <p>The problem with this method is when the UserControl is visible, I cannot click any controls (Buttons, CheckBoxes) in the Window behind the UserControl. I guess I need to make the UserControl transparent to clicks somehow. Is this possible, or is there a better way to add the colour over the Window?</p>