JavaScript FullCalendar color event

HI i make change color event but i got some problems i dont know why event dont change color on grey. I try use json_encode. I do in controller query to checking if event exist in save_event table(its a pivot table). And i dont know how i should do it. I know the easier way will be make input hidden but i think its not practical becouse when on calendar will be 100events so its will be 100 hidden inputs. I write many post about it and i trying do this 3 days and i really dont have any idea to figure it. Maybe someone have tips how do this simple think. On calendar user when joining to event then event should change color to grey.

Script:

<script src="/fullcalendar.js"></script>
<script src=""></script>
<script type="text/javascript">

$(document).ready(function() {

  var base_url = '';
  var color_event = <?php
    json_encode($eventColored);
  ?>

  $('#bootstrapModalFullCalendar').fullCalendar({
    weekends: true,
    header: {
      left: 'prev,next today',
      center: 'title',
      right: 'month,agendaWeek'
    },
     eventClick: function(event, jsEvent, view) {
        $('#modalTitle').html(event.title);
        $('#modalBody').html(event.name);
        $('#eventUrl').attr('href','/home/zapis/'+event.id);
        $("#startTime").html(moment(event.start).format('HH:mm '));
        if (event.end) $("#endTime").html(moment(event.end).format('HH:mm '));
        else $("#endTime").html('');                                        
        $('#fullCalModal').modal();
        return false;
      },

    eventLimit: true,
    FirstDay: 1,
            contentheight : 650,
            editable : true,
            allDay : false,
            aspectRatio : 2,
            slotLabelFormat : 'HH:mm:ss',
            timeFormat : 'HH:mm',
            displayEventEnd : true,
            events: {
      url: base_url + '/api',
      error: function() {
        alert("cannot load json");
      }
    },
    eventAfterRender: function (event, element, view,events_id) {
    if(event.id == color_event){
      element.css('background-color', '#cccccc');                                                                                       
    }
      else
      {
        if (event.title == "Wydzial 1") 
        {
                element.css('background-color', '#378006');
                }
                else if(event.title == "Wydzial 2")
                {
                element.css('background-color', '#ff0000');     
                }
                else if(event.title == "Wydzial 3")
                {
                element.css('background-color', '#73e600');     
                }
                else{
                element.css('background-color', '#0066ff');
                }
              }
    }
  });
});
</script>

Controller:

$eventColos = HomeModel::all();
    foreach ($eventColos as $eventColo) {
       $eventColored =  DB::table('save_events')->where('events_id','=',$eventColo->id)->exists();
    }

  return view('home',['eventColored'=>$eventColored]);

via Mariusz