Vardges,
 не копируйте сообщение целиком
<!DOCTYPE html>
<html>
<head>
  <title>Untitled</title>
  <meta charset="utf-8">
  <style type="text/css">
   body{
     display: flex;
      flex-wrap: wrap;
       justify-content: center;
   }
  .element  {
    border: 1px dashed  rgb(0, 0, 255); padding: 5px; height: 100px; width: 100px;
  }
  </style>
  <script>
window.addEventListener('DOMContentLoaded', function() {
var elem=document.querySelectorAll('.element');
for (var i=0;i<elem.length;i++){
  elem[i].addEventListener('click',F);
}
function F(){
  var tiv = parseInt(Math.random()*9);
  this.textContent = tiv;
  this.setAttribute("tiv", tiv);
  var elem = document.querySelectorAll('[tiv="'+tiv+'"]');
  var color = "transparent";
  if (elem.length > 1) {
    var r=parseInt(Math.random()*255);
    var g=parseInt(Math.random()*255);
    var b=parseInt(Math.random()*255);
    color = "rgb("+r+", "+g+", "+b+")"
  };
  for (var i=0;i<elem.length;i++){
  elem[i].style.backgroundColor = color
  }
}
  });
  </script>
</head>
<body>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
<div class="element"></div>
</body>
</html>