iframe içerisinde :
 
<input type="button" class="btn btn-primary" value="KAPAT" onclick="modalkapat();"/>
  
 
 <script>
        function modalkapat() {
            //window.parent.$("#ContentPlaceHolder1_lbtn_yenile").click();
            //window.parent.$("#ContentPlaceHolder1_txt_Note").val('asdas');
            window.parent.__doPostBack('ctl00$ContentPlaceHolder1$lbtn_yenile', '');
            parent.jQuery.colorbox.close();
            return false;
        }
 </script> 
 
 
 
veya
 
 
 
    <link rel="stylesheet" href="css/colorbox.css" />
    <script type="text/javascript" src="js/jquery.colorbox.js"></script>
    <script type="text/javascript">
        $(document).ready(function () {
            $(".iframe").colorbox({ iframe: true, width: "80%", height: "80%", onClosed: function () { __doPostBack('ctl00$ContentPlaceHolder1$lbtn_yenile', ''); }});
        });
    </script>