$(document).ready(function(){
  var $counter = 0;
  $('.default').click(function () {
    $counter+=1;
    var $this = $(this);
    if ($counter%2==1) {
      $this.removeClass('red');
      $this.addClass('blue');
    }
    else {
      $this.removeClass('blue');
      $this.addClass('red');
    }
  });
});