Make Tech Easier published a guide about making the panels and terminal in the XFCE desktop environment transparent.

How to Make XFCE's Panels and Terminal Transparent

The good thing about XFCE is that it is very customizable, including the ability to change the color of the panel. If you don't like the default color of the XFCE panel, we show you here how to make the XFCE panel transparent and the terminal too. Make XFCE Panels Transparent For this tutorial, we are using XFCE with its default configuration of two panels at the top and bottom of the screen. 

How to Make XFCE's Panels and Terminal Transparent - Make Tech Easier