کد HTML:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
<script>
var n1=16;
function red()
{     
  if(n1>0)
  {
  n1--;
  
  }
  var c=n1.toString(16)+'00';
  document.getElementById('red').innerHTML='#'+c;
  document.getElementById('red').style.background='#'+c;
  
} 
var n2=16;
function green()
{     
  if(n2>0)
  {
  n2--;
  
  }
  var c='0'+n2.toString(16)+'0';
  document.getElementById('green').innerHTML='#'+c;
  document.getElementById('green').style.background='#'+c;
  
} 
var n3=16;
function blue()
{     
  if(n3>0)
  {
  n3--;
  
  }
  var c='00'+n3.toString(16);
  document.getElementById('blue').innerHTML='#'+c;
  document.getElementById('blue').style.background='#'+c;
  
} 
</script>
</head>
<body>
  <table width="200" border="1">
  <tr>
    <td id="red" style="background:#F00;color:#FFF;">&nbsp;</td>
   
    <td id="green" style="background:#0F0;color:#FFF;">&nbsp;</td>
  
    <td id="blue" style="background:#00F;color:#FFF;">&nbsp;</td>
   </tr>
 <tr>
    <td><a href="javascript:void(0)" onclick="red()">change background </a></td>
   
    <td><a href="javascript:void(0)" onclick="green()">change background </a></td>
  
    <td><a href="javascript:void(0)" onclick="blue()">change background </a></td>
   </tr>
  
</table>

</body>
</html>