JSFiddle - React, Tailwind, and code Playground

HTML

<table id="t1">
  <tr>
    <td>1</td>
    <td>2</td>
  </tr>
  <tr>
    <td>1</td>
    <td>2</td>
  </tr>
  <tr>
    <td>5</td>
    <td>6</td>
  </tr>
  <tr>
    <td>2</td>
    <td>3</td>
  </tr>
  <tr>
    <td>2</td>
    <td>3</td>
  </tr>
  <tr>
    <td>2</td>
    <td>3</td>
  </tr>
  <tr>
    <td>3</td>
    <td>4</td>
  </tr>
  <tr>
    <td>3</td>
    <td>4</td>
  </tr>
  <tr>
    <td>3</td>
    <td>4</td>
  </tr>
  <tr>
    <td>3</td>
    <td>4</td>
  </tr>
  <tr>
    <td>4</td>
    <td>5</td>
  </tr>
  <tr>
    <td>4</td>
    <td>5</td>
  </tr>
</table>

JavaScript

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:nth-child(2)').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;
});