update.js.erb

var targetDiv = $('edit_reply_<%= @reply.id %>').getParent('div');
var highlightEffect = function() {
  targetDiv.setStyle('color', '#ffa');
};
new Request.HTML({
  url: '<%= instruction_instruction_item_reply_path(:id => @reply.id) %>',
  update: targetDiv,
  onSuccess: highlightEffect
}).get();