Okay, knowing that you are using illuminant E as your benchmark light-source makes it a lot easier to correct the results of your routine to the way it would look on film.

I have the characteristics of most common film stocks as well as most studio light sources, so can adjust more readily from the results of your algorithm.

So if I understand correctly, you look for as neutral a scene as possible, and then your algorithm analyses and adjusts the colours in those neutral shots as if they were shot under a theoretical illuminant E light source, and captured onto film that did not add its own colour characteristics.

Then use the offsets calculated on those scenes to calculate the offsets for the rest of the reel?