Edit in JSFiddle

window.alert = function(message) {
    $('#overrideAlert').text(message).dialog({
        modal:true,
        title:'Javadomain.in',
        buttons: {
            'OK':function(){
                $(this).dialog('close');
            }
        }
    });
     $('#overrideAlert').css('color','Green');
};

alert('Javascript Alert Message - Green color using jQuery');

<div id="overrideAlert"></div>