The good thing is that formatting a table is very simple. There is no special option for this. Just because tables are frames, they can be handled like any other object we have used until now.
So you might have noticed in the preceding Time for action - that Alt is the key of your success when using Scribus tables. Once you remember this, consider changing the color of the cell or cell-border with the Color tab options of the PP.
To change the cell border you can use the Line tab of the PP (F2). You'll see that there are new options there that let you define the border for each side. Just check the border line you want to use and change the width.
Tip
Ungrouping tables
You can ungroup tables as you wish and manipulate them as with frames. This can look simpler at first glance, but grouping those frames again won't give you the same properties. For example, when ungrouping, you won't be able to modify each side border one by one. So, don't ungroup too quickly...