The start menu is not called "change wallpaper", but "change background picture". Really need to change the theme, many beautiful themes are cute themes of animation type. For example, in the following picture, in addition to the background picture, there are "irregular hollow start menu" and "fully transparent start menu". These are relatively rare in general subjects.

You don't need a Rubik's cube to change the theme, just use your hands. As for how to turn an ordinary theme into the theme shown below, the Rubik's Cube is also uncertain and needs special theme making software.