Here is a way of doing it with javascript:
When you mouse over a table cell, the bgColor of the radio button will change
<html>
<head>
<script type="text/javascript">
function changeColor(color)
{
myForm.myRadio.style.background=color
}
</script>
</head>
<body>
<table width="100%"><tr>
<td bgcolor="red" onmouseover="changeColor('red')" height="20"> </td>
<td bgcolor="blue" onmouseover="changeColor('blue')"> </td>
<td bgcolor="green" onmouseover="changeColor('green')"> </td>
</tr></table>
<form name="myForm">
Mouse over the colors <input checked type="radio" id="myRadio">
</form>
</body>
</html>
Here is how to do it plainly with css
<html>
<head>
<style type="text/css">
<!--
.Radio { background-color: red; }
-->
</style>
</head>
<body>
<input type="radio" class="Radio">
</body>
</html>
or inline css
<html>
<body>
<input type="radio" style="background-color: red;">
</body>
</html>
P.S some of the codes I put might not work, I did not test them