Black_Star,
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.0/jquery.min.js"></script>
<style type="text/css">
#field {
position: relative;
width: 500px;
height: 300px;
margin: 2%;
border: 1px solid black;
}
.square {
float: left;
width: 50px;
height: 50px;
border: 1px solid black;
background-color: red;
transition: all .8s;
}
.yellow {
background-color: yellow;
}
</style>
<body>
<div id="field">
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
<div class="square"></div>
</div>
<script type="text/javascript">
window.onload = function() {
var allDiv = $('#field > div');
function findRandomArr() {
allDiv.each(function() {
$(this).is('.yellow') ? $(this).removeClass('yellow') : Math.random() > .3 && $(this).addClass('yellow')
})
}
setInterval(findRandomArr, 1000);
}
</script>
</body>
</html>