The "HTML" formatting options insert whatever you type into the field so you can do pretty much anything...
Using this...
bgcolor="#15317E" cellpadding="1" cellspacing="0"
The full HTML would look like this...
<td bgcolor="#15317E" cellpadding="1" cellspacing="0">
Use whatever you want [eg: color="red"]
If you use class="xxx", then you define "xxx" in a style sheet.