<html>
<head>
</head>
<body>
<table>
<tr><td style='background-color:red;'>rerer</td><td style='background-color:red;'>rerer</td></tr>
<tr><td style='background-color:red;'>rerer</td><td style='background-color:red;'>rerer</td></tr>
<tr><td>rerer</td><td style='background-color:red;'>rerer</td></tr>
</table>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script>
$("table td").each(function(i){
if($(this).css("background-color") !== $("table td").eq(1).css("background-color")) alert('элемент'+i+' другого цвета');
});
</script>
</body>
</html>