Hi,
Usually, it's best to create a main table to frame the template and act as a container for your design. With that method you can add a style="background:#xxxxxx;" to the table element as attribute, where xxxxxx is the color code number.
The depreciated (no longer recommended) code method is bgcolor="#xxxxxx", which the editor should also accept.
Switching the template editor to Standard mode should give you the toolbars. Look for the icon that looks like a paint bucket. When you select an element, you should be able to use the background color icon to add color. There is also an Insert Table icon as a starting point.
Danno