Love, love, love this game.
One issue I found: the board can only be reset if you have added a green square. I found myself on many level trying to trace out the "empty" path first using the right-click function, and then wanting to erase the board found that the reset button wasn't available until I actually left-clicked a square. Then in the I levels, I realized that pink squares don't trigger the reset button either, there has to be a green square present for it to be available.