This has been driving me crazy. There is always aqua showing around the image! I am trying to completely fill the cell with the image, so there is no gap.
<!doctype html>
<html>
<head>
</head>
<body>
<table style="border-spacing: 0; background-color: black;">
<tr>
<td style="width: 600px; height: 44px; border-spacing: 0; background-color: aqua">
<img style="display: block; width: 100%" src="...banner.jpg">
</td></tr></table>
</body>
</html>