How much leeway do you have on the color palette 
when calling something "monochromatic"?  Since 
colors are part of a continuous spectrum, where 
are the cutoffs?  Know what I mean?  I'm sure 
there are some borderline cases out there.

I only know of ONE cel of mine for sure that is 
100% guaranteed monochrome.  It's a cel of Bantaro 
from Jubei Chan.  He is white.  Pure white.  No 
shading, nada.  (Which is really funny because the 
matching douga has several shaded and highlighted 
areas with various colors.  Heh!)

Yes, learning about cels is always fun.  ^_^

JP