Sanman, PMS 453, is the official color reported in an extremely reliable source, Paul Kunkle's Apple Design which has a detailed accounting of the design history at Apple computer.

Here is a link to an online paper that references it: http://www.landsnail.com/apple/local/design/macintosh.html

I'm sure you know as well as I that the actual implementation of that colour will change the way it appears in the finished product. The fact that it was mixed with a particular type of plastic, means it is entirely likely that it came out a different colour on the Mac. That in part accounts for the PMS representation of the same color on both matte, coated or uncoated materials. Then too there's screen representation, but I presume you are referencing a professional calibration.

That said, I have yet to see an official PMS chip of 453. However, I have a pristine 128K and some accessories which are free from inside coatings and I'm here to tell you the original Mac colour has a green cast to it in certain light. This may explain why the keyboard and cables which are listed officially in Apple technical documents as "medium-brown" have an almost olive appearance. This color appears quite similar to some of the online sources of PMS 453 I have seen as well as that output by my own PMS software. I do not personally have colour-matching hardware.

So, all I can say to you at this point is use 453 as a reference point and alter it with respect to the likely contribution of the base plastic resin composition. Or take an acceptable representation of the original to a colour-matching machine and utilize the resulting colour. I'm sure before picking 453, Manock had the manufacturer mix up some finished samples of several shades before choosing the one that had the "right" look.

Please let us know what you discover either way. Your background sounds fascinating. Do you have a website detailing your current business?