JQuery check box validation

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm3.aspx.cs" Inherits="WebApplication4.WebForm3" %>

<!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 runat="server">
    <title></title>
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js">
    </script>
    <script type="text/javascript">
        $(document).ready(function () {
            $("#btn").hide();
            $('input[type=checkbox]').click(function () {
                if ($('input[type=checkbox]').is(":checked")) {
                    
                    $("#btn").show();
                }
            });
        });
    </script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <input type="checkbox" value="blue" name="color" />blue
        <br />
        <input type="checkbox" value="green" name="color" />green
        <br />
        <input type="checkbox" value="red" name="color" />red
        <br />
        <input type="button" id="btn" value="show" />
    </div>
    </form>
</body>
</html>