Peter,
I will declare my interest. I collect the shades of C8 , C9 and C10-C13. The perf shades are extensive, am sure you agree. Are you a Mulready Group member ? there is postings history on this subject there. I welcome any initiatives on shade measurement systems. Some work has been done by others on spectroscopic measurements, studies of inks, whole topic is a complex field. I have no personal studies record: I use visual comparison together with guidance by experts / dealers. Am interested in any technical hypothesis. What stage are you at with this?
Phil