Hi.
You won't be able to make the cells tansparent, unless you were to set the border color to nothing, and also the alternate coloumn color to nothing. This is because what makes the the table appear as if it has a border is actually a table behind it, so if you were to turn of your alt column colors, you would get the border color instead. It can be done if were to rework your tables so they used css borders, but I think that is a little more work than what your looking for.