$(document).ready(function() {
  var color = '#000';
  var textcolor = 'FFF';
  
  function shadeColor(color, percent) {  
      var num = parseInt(color,16),
      amt = Math.round(2.55 * percent),
      R = (num >> 16) + amt,
      G = (num >> 8 & 0x00FF) + amt,
      B = (num & 0x0000FF) + amt;
      return (0x1000000 + (R<255?R<1?0:R:255)*0x10000 + (G<255?G<1?0:G:255)*0x100 + (B<255?B<1?0:B:255)).toString(16).slice(1);
  }
  
  function randColor() {
    color = (Math.random().toString(16) + '0000000').slice(2, 8);
    textcolor = shadeColor(color,70);
    $('head').remove('style'); $('head').append('<style>body{background: #' + color + ';} .bubble{color: #' + textcolor + '; border-color: #' + textcolor + ';} .bubble:before{border-top-color: ' + '#' + color + ';}.bubble:after{border-top-color: #' + textcolor + ';}</style>');
  }
  
  setInterval(randColor, 3000);  
  
});