$("#myDatePicker").datepicker({
// The hidden field to receive the date
altField: "#dateHidden",
// The format you want
altFormat: "yy-mm-dd",
// The format the user actually sees
dateFormat: "dd/mm/yy",
onSelect: function (date) {
// Your CSS changes, just in case you still need them
$('a.ui-state-default').removeClass('ui-state-highlight');
$(this).addClass('ui-state-highlight');
}
});