I doubt the black paint is to protect the cel
from "stuck sketch" damage....mainly because
that's a lot of extra work for the company...and
if you look at how little they take care of the
cels after it's been used...Course I'm just
speculating...  Also, if it was to protect the cel
from stuck sketch damage, why aren't there more
cels with black paint?  I'd say of the cels I
have, less than 5% are painted black behind.

  I have a few cels with black painting and one of
them is from Jubei Chan.  It's a scene where the
background and a little bit of her outline "lights
up" (for lack of a better description).  

joyka