The central mechanic is easy to understand after a bit of experimentation, but sufficiently deep to alllow non-trivial interactions.
Suggestions for improvement:
1) Automatic saving of solved levels + level select menu showing the already solved levels, so that one does not need to start at level 1 all the time.
2) Level 1 is a good learning by doing tutorial level, but level 2 is IMO already to complicated. It might be better to introduce the button/blocker mechanic in an easier level.
3) The button/blocker mechanic is only color coded, which may it make hard to see for color-blind players. How about using a different color *and* a different symbol for each button/blocker pair?