Notes:

I'm getting some kind of weird (timing-related?) thing where a couple of
pixels show up the wrong color.

Reacting to temperature probably isn't going to be all that interesting,
at least not like this.

Copying edited files to the mountpoint rather than editing directly on the
board kinda seems like the way to go.  Slightly laggier dev cycle, but a
little more deliberate.

Stole get_color_in_range() from a Stackoverflow answer.  Probably going to
get rid of it.

Haven't yet tried driving an external neopixel ring.