not quite there, but it seems like this should work for multicolor
flashing of the boss sprite when it is hit.
multicolored flash works, had to change the boss sprite to white and
black so that the shader could pick up the color (doesn't seem to work
on weird shades of color--stick to well-defined percentages to avoid
float problems; may be able to use Color32 to avoid this problem).

Think I could avoid using the BWBossFlash.mat by defining a material in
the BigBaddieController.cs script.  Not sure whether this is would be
better or worse than the approach involving the making a material in
the Editor.  It may allow for better tracking for git...
Sleep function works globally.  It's called when the PC is knocked
back.
more cowbell