If it works like it does in Windows 7. open WB config and select the default Windows skin.
Click on the Background button.
Click on Explorer Backgrounds.
Pick a background and click on Apply Style. You should now have the default Windows theme with the explorer background of your choosing.
Have a nice day.
P.S.. There are thousands of Win 8.1 users who have no trouble running WindowBlinds on that OS. Perhaps you have given up too soon. What sort of trouble are you having and did you submit a ticket to support?