changes with mouse click

There is an onEventClick event handler which you can use to call a server-side endpoint using AJAX (to make the change persistent). You can also change the event color using DayPilot.Scheduler.events.update():

dp.onEventClick = function(args) {
  $.post("changeColor?id=" + args.e.data.id, function(data) {
    args.e.data.backColor = "red";
    dp.events.update(args.e);
  });
};