If you wrap you widget with a "div" html tag, you can set the background to a color, image, or any CSS option.
Here's an example:
<html>
<head>
<title>Widget Background</title>
</head>
<body>
<div id="ioWidgets" style="background-color:red;">
<script type="text/javascript">document.write(unescape("%3Cscript src='" + "http://www.iobridge.com/widgets/io.js?SVTwVdVUZRg3' type='text/javascript'%3E%3C/script%3E"));</script>
</div>
</body>
</html>
Although red is a little much...Just for an example...You might want to try "white". I hope that is what you are looking for.