You see big bubbles in the sky. They are blue/purple. The sky is cyan/light blue. You stand on a blue/purple transparent bridge. under you is a sea of a blue/purple slimey liquid. In the background is a bubble city with blue spren. In the bubbles are filled with people's stuff. Blue spren (see homebrew species) live in the cities. In the cities are portals to other realms. You can only have this background if you are a blue spren yourself.