Microsoft just released a new update and possibly the last update KB4539602 for Windows 7. It fixes the black wallpaper issue.
If you are still using Windows 7, you might have noticed that with the 'Last' update KB4534310 caused the wallpaper to go black. No matter the wallpaper you set, the bug in KB4534310 caused Windows 7 to force replace the wallpaper with solid black color. To fix this issue, Microsoft rolled out another last update. After you install the update, the black screen issue in Windows 7 should be fixed.
Like always, you can directly download the update by going to "Control Panel → Windows Update" and clicking on the "Check for updates" button. If you are facing problems with this approach, use the links below to download KB4539602 update offline installers.
Direct Download KB4539602 Offline Installer
To make things easier for you, I found the direct download links for KB4539602 for both Windows 7 32-bit and 64-bit systems. Depending on your system type, download the update using the below links and install it like any other Windows software. After installing, restart the system and you are good to go.
KB4539602 x86 (32-bit) offline installer (download size: 205.7 MB)
KB4539602 x64 (64-bit) offline installer (download size: 314.1 MB)
If you want KB4539602 download links for Windows Server based systems, go to the Microsoft update catalog website to find the appropriate links. All you have to do is click on the Download button next to the appropriate version.
KB4539602 Change Log
This non-security update includes improvements and fixes that were a part of KB4534310 (released January 14, 2020) and also includes these new quality improvements as a preview of the next Monthly Rollup update:
Addresses an issue that might cause your wallpaper to display as black when set to Stretch after installing KB4534310.
That is it. I hope the update fixes the black wallpaper issue in Windows 7.