I completed the game.
The mecanics and leveldesign are well made, the difficulty balanced. The minimalist art style and audio fit the game perfectly. Good polish.
Not a lot to critics to do, beside maybe that the main mechanic is not 100% intuitive. On the first levels I got confused several times about which color of the orb replace which (its exterior being replaced by interior but the shape of the "orb" doesn't really conveys it).