I only have a Mac, so I can’t play it. But that would be some kind of feedback as well. Please check the Windows box on your Edit page, so people will know what it is :)
Other than that, I think motivation to play could include an online high-score leaderboard, unlocking new stuff when playing well (like new color palettes), and maybe some easter eggs. You could also add a meta layer where the letters are part of a puzzle, or words of a story, or something like that.