Use this template to make it quick to create a unsub footer.
You may change the text in the replacement tags for what text you want the unsubscribe link to have.
With transparent background:
<tr>
<td>
<% Unsubscribe from our newsletters here. %>
</td>
</tr>
With background (change the background color on the second line):
<tr>
<td style="background-color: #000000;">
<table role="presentation" cellspacing="0" cellpadding="0" border="0" width="100%">
<tr>
<td style="padding: 20px; font-family: sans-serif; font-size: 15px; line-height: 20px; color: #555555;">
<% Unsubscribe from our newsletters here. %>
</td>
</tr>
</table>
</td>
</tr>