function swapControl(id, state, color) {
    uppath = 'images/btn-up-'+color+'.jpg';
    downpath = 'images/btn-down-'+color+'.jpg';
    
    el = document.getElementById(id);
    if(state == 'down') {
      el.style.background = "url('"+ downpath +"') no-repeat";
    }
    else {
      el.style.background = "url('"+ uppath +"') no-repeat";
    }
}