Hello again,

During testing the app, I noticed that it is a little confusing the fact that the existing numbers look very similar to the ones entered by the user. I can see that the cells where the user needs to enter numbers have a subtle border, but it’s not very noticeable while playing the game. Also, according to Nielsen, it could be considered that this case violates heuristic #1: “Visibility of system status”, since the interface doesn’t clearly communicate the state of the cells (editable vs. non-editable). I have attached a picture to make my point clear.
As a simple solution I would suggest to just make the background of the existing cells gray. This way, users would easily tell which cells are editable and which are not.

Let me know what your thoughts are.

Kind regards,
Bill