Click the "Apply" button in the screenshot and then reboot your machine.
If the silver default "Windows XP" is not applied when you restart, open the Display Properties again > click the "Themes" tab > select "Windows XP" in the drop-down list (if already selected, just open the drop-down and click on Windows XP to invoke the "Apply" button) > click "Apply".
If all is well, you will be looking at the default Windows XP "Blue Luna" shell theme. Simply click the "Appearance" tab > select "Silver" from the Color Scheme list as shown in your screenshot > click "Apply".
There is a known issue with WindowBlinds 5, where (in some cases) the Display Properties dialog will not incorporate fully until a reboot after attempting to use it the first time after installing WB 5. I saw this while testing the beta versions previous to official release, and have continued to see it when doing clean installs. Once you get the Display Properties fully incorporated after rebooting, there should not be any more issues with regards to using the dialog to change the shell style and colors.
Note - if this does not fix the issue, then try applying the "Windows Classic" from within WB 5 configuration panel > open Display Properties\Themes tab > select and apply "Windows Classic" there > reboot > reopen Display Properties\Themes tab > select and apply "Windows XP" > use Appearance tab to select and apply the "Silver" color scheme.
I hope this helps. 
