Traditionally, it is frowned upon to customize standard form controls due to the inconsistency in appearance across various web browsers. You can find some examples of this issue here: .
However, one approach that has shown some success is setting the background color using an RGBA value:
<!DOCTYPE html>
<html>
<head>
<style>
body {
background: #d00;
}
select {
background: rgba(255,255,255,0.1) url('http://www.google.com/images/srpr/nav_logo6g.png') repeat-x 0 0;
padding:4px;
line-height: 21px;
border: 1px solid #fff;
}
</style>
</head>
<body>
<select>
<option>Foo</option>
<option>Bar</option>
<option>Something longer</option>
</body>
</html>
In Google Chrome, a gradient effect may still appear over the background image when using rgba(r,g,b,0.1). To minimize this, choose a color that complements your image and set the alpha channel to 0.1.