base.xml ... to go in the theme root dir :-)

<mythuitheme>

  <window name="backgroundwindow">
    <imagetype name="backimg">
      <filename>background.jpg</filename>
    </imagetype>

    <imagetype name="logo">
      <filename>button_background.jpg</filename>
      <position>0,0</position>
          <alphapulse min="180" max="180" change="0"/> 
    </imagetype>
  </window>

</mythuitheme>