eddin,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.red{
background-color: rgba(0, 128, 0, 1);
}
</style>
</head>
<body>
<form name="main" id="main" >
<select name="sel">
<option value="0">Выберите</option>
<option value="24">Раз</option>
<option value="25">Два</option>
<option value="26">Три</option>
</select>
<select name="sel">
<option value="0">Выберите</option>
<option value="24">Раз</option>
<option value="25">Два</option>
<option value="26">Три</option>
</select>
</form>
<script>
window.addEventListener('DOMContentLoaded', function() {
var form = document.querySelector('#main'),
select = form.querySelectorAll('select');
form.addEventListener('change', function(event) {
event.target.name && event.target.name == 'sel' && event.target.classList.add('red')
});
});
</script>
</body>
</html>