I agree Bill.
I'm sure that color charts and just shooting the film and interpreting the results can be informative, but not nearly as illustrative as a wedge spectrograph. A series of those can be compared against each other almost immediately, and without much deduction. Their look says it all.
I'm convinced we can make something very inexpensively. All we're doing is projecting a spectrum onto a piece of film, through a step wedge. It's just a matter of buttoning it all up and working within some parameters.
First though, I think we really need to wrap our heads around the design and understand that (in 3 dimensions) more clearly. Hopefully some Q&A will get us there fairly quickly.