Globus,
а так ?
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
</head>
<body>
<style>
div.images { opacity:0.5; }
:checked + div.images { opacity:1; }
</style>
<form method="POST" action="" class="wpcc_form wpcc_form_2">
<div class="1">
цвет
<label><input type="radio" name="m" checked="checked">
<div class="images"><img src="img-1.jpg"></div>
</label>
<label> <input type="radio" name="m">
<div class="images"><img src="img-2.jpg"></div>
</label>
</div>
<div class="2">
форма
<label> <input type="radio" name="p">
<div class="images"><img src="1a-img.jpg"></div>
</label>
<label><input type="radio" name="p">
<div class="images"><img src="2a-img.jpg"></div>
</label>
<label><input type="radio" name="p">
<div class="images"><img src="3a-img.jpg"></div>
</label>
</div>
</form>
</body>
</html>