#JS 
$$("td.filterfeedlink > a").each(function(element){ // Find filter feed links 
	
	Event.observe(element, "click", function(event){ // Register them to listen
		
		$$("td.filterfeedlink").each(function(el){
			if(el != this){
				el.up().removeClassName("turnwhite");
			}
		});
		this.up().up().addClassName("turnwhite"); // Clicked element -> white
	});
});

#HTML
<table>

  <tr class='filterfeed'>
    <td>
      Info A
    </td>
    <td class='filterfeedlink' >
      <a href="#" onclick="new Ajax.Request...">Filter</a>
    </td>
  </tr>

  <tr class='filterfeed'>
    <td>
      Info B
    </td>
    <td class='filterfeedlink' >
      <a href="#" onclick="new Ajax.Request...">Filter</a>
    </td>
  </tr>

  <tr class='filterfeed'>
    <td>
      Info C
    </td>
    <td class='filterfeedlink' >
      <a href="#" onclick="new Ajax.Request...">Filter</a>
    </td>
  </tr>

</table>