The background (sky) picture is just a very tiny square that all you can do is fill with a color, maybe a very small pixel design that would I assume be stretched out and look terrible (or maybe repeat endlessly and also look bad). The background (floor) of the wara wara Plaza is a decently sized image that you could alter as you like, but it's structure in the home menu is tesselated in an odd way that kinda circles out? Hard to explain, but the point is, it's hard to design for, as it's a bit hard to picture how the design will be repeated along the floor. Still it might be worth exploring possible designs than can work here beyond just the recolors of the original design that I've been doing.