Just use the cellspacing
attribute.
<div style="width:750px;">
<table style="width:30%;" border="0" cellspacing="0">
<tr>
<td style="width:40%; background-color: red; height:150px;"></td>
<td style="width:60%; background-color: yellow; height:150px;"></td>
</tr>
</table>
</div>
First result in google in this similar question: https://stackoverflow.com/a/2279510/22492703