function changeColour(elementId) {
    var interval = 1000;
    var colour1 = "red", colour2 = "#FFFF00";
    if (document.getElementById) {
      var element = document.getElementById(elementId);
      element.style.color = (element.style.color == colour1) ? colour2 : colour1;
      setTimeout("changeColour('" + elementId + "')", interval);
    }
  }