What do you do when, after investing hours in a puzzle, you realize that somewhere along the line you made a mistake? You don't have the heart to start over, but, since you don't know where your mistake is, you can't continue.
CrossPix has a way out. If you hold down the shift and control keys and click in the open area at the top left corner of the puzzle, then all incorrect cells will revert back to the starting color.
However, (you know there would be a catch, didn't you) to discourage overuse of this feature, not only is every wrong cell reset, but the entire row and column of every wrong cell will also be reset. You have been warned!