You may have a Texture selected which would modify all WB themes. Your Textures should be none:
Also Start10 should look like this:
If you match here then the easiest first try at a fix would be:
1. Open WindowBlinds and set the theme to Default and reboot.
2. Go to your Stardock My Downloads and download and run the latest WB setup and reboot.
3. Try to apply a WB theme and see if problem is gone.