Thanks! All of the graphics, colour palettes and sounds are procedurally generated which makes the game small in file size and endless to explore.

Not quite endless, I found an 3 edges of the space. Couldn't move beyond.

The terrain is bounded by walls (a design decision to keep users from getting too far away from portals) but you can discover new palettes and worlds forever, by continuing to step through unexplored portals.

I wondered about this, too, after running into the edges. I thought they would have made it "infinitely" generating, like with a periodic boundary or some tessellated space.

Looks like the sound is generated based on various parameters in the game, like the height of the grass and color of the field.