experimenting with main mechanic

- showing colors
- tapping behaviour
- stacking behaviour
nicer renderBlock fuction

easier to change each part of the block design
tweaking mechnics, discovering it isn't working

falling blocks don't seem to capture the stroop effect
very well;  I've tried many permutations, but none are
"fun" to play or particularly challenging.  This is the
best I arrived at.

From here, I may change the mechanics significantly.