In addition to defining background colors you can also add background graphics to your tables. For example, you can insert a single large graphic behind a table like a "watermark", or you can tile a small graphic to create a repeating pattern or texture as a background for the table.
You can apply a background graphic to a single cell of a table by using a single-cell nested table (inserting one table inside another) and applying the background graphic to the nested table.
Table Properties (Reference)
How table sizing works (Reference)