Actually if you look at the code you will see that the page is made up of multiple tables...
The thread display page is made up of at least 6 plus one for each post tables....
Header, Breadcrumb, Top Orange Header, Posts (X times), Bottom Orange Footer and Footer.
By using these layered tables we can increase the perception of a faster download time. You can start reading and navigating before the page is finished downloading and rendering. This is a common technique used on many sites. The reason being is that a table cannot be rendered until it is completely downloaded. By breaking things up you will speed rendering up.
Let us examine each portion in turn skipping the header and the footer.
This table has two cells. The first contains the actual breadcrumb path (i.e.: sitepoint forums > client side scripting > this dump html) as well as the Print, Email and New Post links underneath that. The other contains links to the next and previous threads if appropriate.
This is the table you expressed interest in. The code is simple.
If you can tell there is no cellspacing on this table. This accounts for the lack of white borders in the orange bars.
<table width="98%" border="0" cellspacing="0" cellpadding="4">
<TD valign="middle" width="175" nowrap>
<FONT face="verdana,arial,helvetica" size="1" color="#FFFFFF" class=thtcolor><B>Author</B></font>
<TD valign="middle" width="100%">
<table width="100%" border="0" cellpadding="4" cellspacing="0">
<td valign="middle" width="100%">
<FONT face="verdana,arial,helvetica" size="1" color="#FFFFFF" class=thtcolor><B>**Thread ** </B></font>
<FONT face="arial, helvetica" size="2" >*</font>
<A HREF="newreply.php?action=newreply&threadid=14005"><IMG SRC="images/reply.gif" BORDER=0 ALT="Post A Reply (Alt-R)"></A>
This is a table for each post. It is comprised of a wrapper and an individual table for each post. The wrapper has a cellspacing of 1 and two columns. The cellspacing of 1 is what creates the white borders. The first column contains Author information. The second contains the post icons and the actual message. Each cell is actually one or more cells.
This is basically a duplicate of the Orange Header it just contains slightly different information.
Setting background colors should work on rows, cells and tables themselves. The hierarchy is that cells are highest priority, then rows, then the table then the page itself. However, some browsers may not be HTML 4.0 compliant and not render the pages properly.