Windows 10 has three different types of backgrounds; the lock screen background, the desktop background, and the sign-in screen background. Of these three background images that appear on your screen, the sign-in screen background cannot be changed unless you use an app. If you leave the background untouched, you will always see the Hero wallpaper that is one of the defaults in Windows 10. If you aren’t too fond of the wallpaper and would prefer to not have any image appear on the sign-in screen, here’s how you can disable it altogether.
To turn the background on the sign-in screen off, you must be running the 1511 build of Windows 10 released in November 2015. If you aren’t sure what build you have, use the version check tool to find out.
If you’re on the right build, open the Settings app and go to the Personalization group of settings. Click the Lock screen tab and scroll down to the ‘Show Windows background picture on the sign-in screen’ option. Turn it off and the sign-in screen will no longer show any image.
Instead, it will show you solid color filled background. To customize the color, go to the Colors tab in the Personalization group of settings and select a different one. You can select one of the pre-defined colors or you can have Windows select one that matches your desktop wallpaper.
Turning the feature On/Off is easy and you won’t need to sign out and back into Windows for the change to take effect. Maybe in the not too distant future, Microsoft will let users choose an image for the sign-in screen background too.