title: imagebutton with @null background (transparent)
body: <p>I have a imagebutton with a image source with transparency, but the background color of the imagebutton is the tipical gray button color.</p>
  
  <p>I want set background = @null and this works fine.</p>
  
  <p>But, when i press this imagebutton i can not see the color that indicates that I am pressing the button.</p>
  
  <p>if i remove background = @null when i pressing the button, change the color for the user know you are pressing.</p>
  
  <p>I read that you can make a xml with 3 images specifying when the button is pressed, when this normal and when it has focus. But I think exists an easier way to do.</p>