Hello,
Sorry to hear you are having issues. Yes, it possible, use the slider instead. You can set it for all the Fences or individual Fences. Example in screenshot below. Inside Fences 4 configuration window.-> Color & appearance->Background Style and Color-> click on the drop down arrow to select individual Fences to change or select "All Fences" to change all-> Transparency slider->Slider to left to adjust to what ever transparency setting you wish.
Thanks
Basj,
Stardock Community Assistant.