function changeColour(elementId) {
  var interval = 500;
  var colour1 = "#cf3f3f", colour2 = "#00481e";
  if (document.getElementById) {
   var element = document.getElementById(elementId);
   element.style.color = (element.style.color == colour1) ? colour2 : colour1;
   setTimeout("changeColour('" + elementId + "')", interval);
  }
}