Zendoku

this is very pretty, but this doesnt work easily. I tried the undo button to clear a square, when I accidently hit a square I did not mean, and it did not work on the cell I wanted it to, but took everything else off. I tried doing the instructions again to undo, didn't work. I want to be able to click on a number, then go click all the squares I want for that number, not go back and forth each time. This did not have that option, unless it is hidden.

But I would like to be able to turn off the color change when I correct numbers are placed on the board.