I have had several questions about the interior borders of tables as we have moved to Moodle 2.1 from 1.9. In the new HTML editor is not as clear how to edit table properties and the default table border color for interior borders seems to be set to white. Once you have a table there are a lot more options, but you have to right click on a cell when editing a cell. Then you get a whole menu of options. The screen cast allows you to see how to change the default color of you borders to black in the table you are working on.