Took me a moment to figure out what I am supposed to do, but the art direction and sound design was awesome:) Great job! Have you composed all these musical pieces?
Also a little suggestion, it would be good for the cursor to turn white (instead of black) when over black clouds at the border of the screen:) or to be able to use a keyboard, since it is already used during the minigame anyway.
Shaders sounds like the right way to do it, but since I am not very skilled with them (and also it is a jam piece, so there are really not many benefits to doing things the right way), I would probably just get the position of the mouse on the screen, raycast from there to find out if the cursor is over the cloud and if yes then swap the sprite for the white one. Seems like the easiest way to do it:)