[Nexus]

https://jsfiddle.net/aecoxyyw/3/

<table id="t1">
  <tr><td>1</td></tr>
  <tr><td>1</td></tr>
  <tr><td>5</td></tr>
  <tr><td>2</td></tr>
  <tr><td>2</td></tr>
  <tr><td>2</td></tr>
  <tr><td>3</td></tr>
  <tr><td>3</td></tr>
  <tr><td>3</td></tr>
  <tr><td>3</td></tr>
  <tr><td>4</td></tr>
  <tr><td>4</td></tr>
</table>
<script>
(function(){
  var COLORS=['red','green','blue'],
      rows=document.querySelectorAll('#t1 tr'),
      last_value,
      color_index=-1,
      change_index=true;

  [].forEach.call(rows,function(row,index){
    var val=row.querySelector('td').innerHTML;
    if(val==last_value)
      return change_index=([row,rows[index-1]].forEach(function(node){
        node.style.backgroundColor=COLORS[color_index];
      })||true);

    if(change_index)
      color_index=!COLORS[++color_index]?0:color_index;

    change_index=false;
    last_value=val;
  });
})();
</script>