Amillusion currently offers 8 menu themes you can choose from the canvas in the waking version of Danaë's Room. The current menu theme will be displayed on the canvas in the real world until you change it. These menu themes also effect the saving theme played when you are on Danaë's PC and even the paintings displayed in her room. Here are how you obtain them:
You start the game with this theme.
In Magic Area, Go north-east and interact with a big legged sphere to get the theme.
Find and pass between two columns of grass in Bubble Forest to get the theme.
Enter the Sequoia Lucky Forest, where the Shamrock effect is obtained. Interact with one of the spinners on the trees to land on the blue space marked with a question mark to get the theme.
This menu theme will be automatically received after hitting the heart in Crazy Maze 5 times with the Brambles key.
Find and interact with a sign on one of the cubes in EPACSE to get the theme.
Feed the bird 7 times in the Nursery to get the theme.
In one of the rooms of Residential Corridor World is a sunflower NPC, interact with them to get the theme.