title: JavaFX 2 custom popup pane
body: <p>The JavaFX 2 colour picker has a button that pops up a colour chooser pane like so:</p>
  
  <p><img src="https://i.stack.imgur.com/fKAHT.png" alt="JavaFX 2 colour picker"></p>
  
  <p>I'd like to do something similar, in that I'd like a custom pane to pop up when the button is clicked on and disappear when something else is clicked (in my case, a few image thumbnails). What would be the best way of achieving this? Should I use a ContextMenu and add a pane to a MenuItem somehow, or is there something else I should look at?</p>