Thanks for the note. Earlier versions did make use of dithering to further distinguish the block types. With the scrolling stack, it ended up too busy and a bit strobe-y.
I will explore further possibilities for a future update.
Yeah, I can see what you mean about the strobe on the grayed-out bottom row. The canonical way around dither strobe on the Playdate (assuming 2x2 dithers) is to scroll in two-pixel increments. If that eats into your smooovness (as I imagine it might), you might have to get resourceful. Two ideas I can imagine:
Failing that, just have an accessibility toggle that, like, blacks out the center of the circle, cross, and heart, or draws them as white-on-black. Changing those three blocks would help distinguish heart from diamond, circle from both square and diamond, and the cross, well, that's just for symmetry since there are six blocks.
Oh, and a music toggle would be nice.