I wouldn't de-emphasize color matching too much.

I had the experience a few months ago of selling 
a cel, at which time it was a bit controversial 
whether it was a production cel or a fan cel.  I 
believed that it was a production cel, as I had 
been told, both others were not so sure (I ended 
up selling it as a "possible fan cel").

The lesson from this was that what seemed to make 
the cel controversial was color matching -- some 
folks thought that a couple of the colors were 
off by a shade or two.

People seem to be quite sensitive to subtle color 
variation.