Tetris on RGB matrix

That's awesome. The diffuser isn't bad - you need some kind of diffuser, otherwise you can see the individual colors in each LED (like red/green dots inside the yellow). Vellum from art store is considerably better than straight up paper. It's a little clearer, looks more even, and less obviously cheap.

The diffuser (and frame around it) also lets you hide some super bright lights along the perimeter, which you could do a light show with (ie, a few bright flashes right after a tetris, making it harder to see the game action - this is legit tactic in arcade games, used very effectively in pinball)

Really, no need to excuse your paper difuser - your tetris gameplay, on the other hand... ;-)