The desktop background that is chosen as per preference when using desktop in Windows 8.1 can also be set to show on Start screen that has various tiles/apps.
To do this :
Right click on taskbar and select “Properties”.
Next, go to the Navigation tab and check the option “Show my desktop background on Start”. Hit Ok to save the changes.
Now access the Start screen (either through the Start button on desktop taskbar or by using the Windows key).
The chosen background now will be visible.