var oldId = null;

  function showDiv(id) {
    if (oldId!=null) {
     $("#"+oldId).slideUp('fast');
     var oldBut = document.getElementById(oldId+"-but");
     oldBut.style.backgroundColor = "";
    }

    var button = document.getElementById(id+"-but");
    button.style.backgroundColor = "#797979";
    $("#"+id).slideDown('slow');
    oldId = id;
  }