Hi Hari,
Please use the below code to change the color of checkbox.
<html>
<title>Hamendra</title>
<head>
<style>
.hamendra-checkbox {
background-color: #0000FF;
}
</style>
</head>
<body>
<input type="checkbox" id="checkbox1" class="hamendra-checkbox" />
</body>
</html>
Thanks,
Hamendra