vBulletin's WYSIWYG editor will convert a table tag to BB-Code because a TABLE BB-Code exists. If you are using the vBulletin TABLE BB-Code, you will need to look at their docs, tutorials, or community to find out how to apply a background color.
In VaultWiki's TABLE tag, it's really easy, but the syntax is completely different from vB's:
[table] style="border: 1px solid #000; width: 62%"
| style="background-color: red" | background is red
| background is not red
|background is red||background is not red|