Fun game and somewhat hard. I did not figure out how to use z but my guess is the timing.
Also edges would not trigger coloring.
I got a crash report for you too:
Error
src/Enemy.lua:51: attempt to index local 'target' (a nil value)
Traceback
[love "callbacks.lua"]:228: in function 'handler'
src/Enemy.lua:51: in function 'update'
src/states/PlayState.lua:112: in function 'update'
main.lua:79: in function 'update'
[love "callbacks.lua"]:162: in function <[love "callbacks.lua"]:144>
[C]: in function 'xpcall'