Trying this iteratively as I learn.

This version just fills the screen regardless of keypress state (which is the easy part).  I'm filling one VRAM block at at time, but because you Hack can't load 16 bit unsigned values, I can only block the first 15 bits of every 16 bit block.

Yay for pinstripes?
And people said nothing would ever come of my negativity!

Pshaw.
Finish first working version of Fill