function setTrBg(id, color1, color2) {
  var tables = document.getElementById(id).getElementsByTagName('table');
  for (i = 0; i < tables.length; i++) {
    var trs = tables[i].getElementsByTagName('tr');
    for (j = 0; j < trs.length; j++) {
      trs[j].style.backgroundColor = j % 2 == 0 ? color1: color2;
    }
  }
}