Memophenal #2 of more
As far as backgrounds of table components are concerned, the visual organization of a table is rather straightforward. Each component lives, dependent on its type, in one of the layers of a stack as shown below.
The direction of view is top-down, so the backgrounds of lower layers are only visible as far as the components above it have a transparent background (which is the default).
Tables defined by (Multi)Markdown code don't contain column or column group elements. That makes the model even more simple.