In order to trigger Windows 10 into changing the default theme, you will need to play around within the registry. Making the necessary changes is relatively straight forward and easy to follow, but entering into and modifying entries within the Windows Registry can cause problems if done incorrectly. Be warned.
Step 1: Launch the Registry Editor in Windows 10. Type Regedit in the search bar and click Yes when the OS requests for permission to run the request.
Step 2: Within the Registry Editor navigate to the following entry: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize.
Some users may find themselves in a position where they don’t actually have an end sub-folder called Personalize. If this is the case, then worry not. Simply create a new key named Personalize. To do this right click on the Themes key and select New > Key and name it Personalize.
Step 3: Right-click on the new Personalize key and select New > DWORD (32-bit) Value.
Step 4: Set the new DWORD key name to AppsUseLightTheme.
Step 5: In the Value data text entry field, make sure the value is set to ‘0’. It should have this value as default.
Step 6: Repeat steps 1 through 5 again, but this time for the following key: HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize.
Step 7: Exit the Registry Editor.
Step 8: Log out of Windows 10 by selecting Start Menu and then tapping on your user profile photo and choosing Sign out.
Congrats! You’ve now taken Windows 10 to the dark side.