Hello Willett, Rosemary,
Following up on your issue, if your IT department's previous efforts have proven ineffective, the underlying issue is almost certainly a corrupted .theme configuration file prioritizing system defaults during the logon initialization phase, or a hidden registry-level configuration silently overriding your local GUI selections. To align with official Microsoft deployment documentation for managing desktop environments, we must bypass the standard Settings application and forcefully define your configuration at the registry and local application data levels to ensure persistence.
You or your IT administrators must open the Registry Editor and navigate directly to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\ActiveDesktop to verify that the NoChangingWallPaper DWORD is either entirely absent or explicitly set to 0 . To strictly enforce your solid color preference and prevent the desktop window manager from defaulting to a system image, proceed to HKEY_CURRENT_USER\Control Panel\Colors and modify the Background string value to your desired RGB code, utilizing a format like 0 0 0 for solid black. Immediately after securing these registry values, open File Explorer, navigate to %USERPROFILE%\AppData\Local\Microsoft\Windows\Themes, and permanently delete all .theme files within this directory, specifically targeting Custom.theme and any roamed template files. This completely eradicates the corrupted instructional files the Windows Shell is mistakenly relying upon upon login. Restart the explorer.exe process or log out completely to force the system to generate a clean configuration state based purely on your registry directives.
Hope this answer brought you some useful information. If it has, please consider accepting the answer so that other people sharing the same issue would benefit too. Thank you :)
VP