Great little game and seems you fit in quite a lot of stuff (high scores, skins, achievements, save system) in one week! Thought I'd be safe when I had the same color and reversed the cube, but during that time the color switched and I died :D Perhaps capping the speed would make it easier to play as I assume you have something in your update method that constantly adds speed.
For mobile I think it could be a nice game! Good job!