fmr beat me to it, but I'll post it anyway...
Empty Fill can be opaque if the element's fill has a background color. Any non-solid fill can be. Pen 0 makes the fill background transparent. In the AC library table objects, the background parameter is under the 2D Representation heading.
There is a Fill Background Color display option which controls to how backgrounds are displayed, if they aren't using pen 0.
In the attached image, the table object has background pen 0, and the counter slab has BG pen 91; both are using Empty Fill. The display options are cover fills: vectorial, and Fill Background Color: By Elements' setting.
HTH,