it called callback_column it will "process" the column before it shown to user.
here's example
public function webpages()
{
$c = new grocery_CRUD();
$c->set_table('status');
$c->columns('estado','email_propietario');
$c->callback_column('estado',array($this,'_callback_active_state'));
$output = $c->render();
$this->_view_output($output);
}
public function _callback_active_state($value, $row)
{
if ($row->estado == 'pendiente'){
return "<pre style='color:red'>".$row->estado."</pre>";}
else {return $row->estado;}
}