Highlighting works for some cells, but not others

Highlighting works for some cells, but not others

I'm dealing with this script for a while now, I couldn't fix this. Some cells are highlighted some are not. When you make a selection from the select box, the matching value's supposed to be highlighted. it only works for some cells.  Can I get some help, please? 
For example, if you select 1, it works. but it doesn't work for 2,3

. 
  1. $("select").change(function () {

  3.   var selectIndex = $(this).parent().index();
  4.   var value = $(this).val();

  6.   $('th', '.table2').each(function() {

  8.    if($(this).index() === selectIndex) {

  10.       if($(this).attr('value') ==  value) {
  11.         $(this).css('background-color', 'yellow');
  12.       }
  13.       else {
  14.        $(this).css('background-color', '');
  15.       }
  16.     }
  17.     
  18.   })
  19. });