I've had NightSky on Steam for quite a while; big fan of the game. As with the most recent Humble Bundle, I decided to give it a try on my Android tablet (Google Nexus 7) and I've run into a few issues with the controls. I'm very thankful that you added in multiple control schemes, but I think they could be improved further.
'Swipe' mode doesn't really work for me, since broad gestures don't always seem to make the ball go full speed, and yet in levels where you can make the ball turn very very quickly (blue glow), I have a hard time not making it spin full speed with small gestures.
'Tilt' is probably the best control scheme so far (for me), but I have a hard time keeping the ball to stay still! Holding the tablet in my lap, keeping the ball on a platform while clicking on other objects requires nudging the tablet every which way and it's very awkward. I even put the tablet down on my (hopefully level) basement floor, and the ball rolled slowly to the right!
Selecting 'Digital' crashes the game, but enables when I start the game up again. It worked for the most part, but I felt like it kinda defeated the purpose of having a touch device in the first place. Not your fault, just personal preference. I also managed to accidentally restart a level while trying to move around!
What I'm suggesting is that you add the ability to calibrate each control scheme. For example, 'tilt' should have a way to set an absolute "down" direction, a deadband for keeping the ball still, and possibly a way to set how far the player has to tilt to go full speed. I don't mind rotating my tablet a full 80 degrees if it means I get the full range of motion that's comfortable for me.