Debugging a page at:
If you view this page in Safari, you'll notice the lower right quadrant is a big red, blank square. However, there's an IFRAME element there, as the sole bit of content within a table cell, that isn't showing. It's width and height are both set to 100%.
Some debugging has led me to believe that Safari considers the dimensions of the IFRAME element to be 0, when width and height are set to percentages. If I change the width and height to pixel dimensions, then the IFRAME shows, at those dimensions, and the background of the table cell shows as planned. If I add other content to the table cell which contains the relatively-dimensioned IFRAME, then that content shows up and the table cell expands just enough to contain this content.