This matter is discussed in a thread here

Basically in order to make a cell completely transparent it is recommended to load an entirely blank Logo into your Fast Dial Cell.

So

1. Download a blank Logo from UL.

From here or here.

2. And then in Properties advanced simply load in your saved Fully Transparent Blank Logo to the cell.

The cell will then be simply invisible.

You can possibly chose to have the Title of the Cell visible on hover to be able to identify the cell.

This is a good way to organise your Fast Dial page if you are more interested in seeing the Background Image than a number of Logos.