All shell profiles in Windows Terminal use a black solid color background by default.
If you like, you can change the default background color, set to use the desktop wallpaper as the background image for profiles, or use a selected custom background image for profiles.
If you select to use the desktop wallpaper or custom background image for a profile, you can select the stretch mode, alignment, and opacity to use for the background image in the Windows Terminal profile.
This tutorial will show you how to change the background color and image of Windows Terminal profiles for your account in Windows 10.