How to apply colours for each events in full calendar js?

Question

I want to show multiple events with different colour for each. Here two ajax response have displayed in calendar. But all the events shows only green. The Second events also visible in green colour. How to show each events with different colours?

My code is as follows:

$('#calendar').fullCalendar({

      events: function(start, end, timezone, callback) {
         $.ajax({
            url: url1,
            dataType: 'json',
            success: function(response) {
                 var events = [];
              $(response.data).each(function() {
                 events.push({
                  title: $(this).attr('title'),
                  start: $(this).attr('start'), // will be parsed
                  color: 'green'
                 });
              });
             callback(events);
            }
         });
         $.ajax({
            url: url2,
            dataType: 'json',
            success: function(response) {
                 var events = [];
              $(response.data).each(function() {
                 events.push({
                  title: $(this).attr('title'),
                  start: $(this).attr('start'), // will be parsed
                  color: 'red'
                 });
              });
             callback(events);
            }
         });
       }
       
   });