I was one of the guinea pigs in reference to the whole evolution of paint matching machines. The first ones were very expensive continuous spectrum plotting IBM units about 8 ft tall and 8 wide using a rotating neutral density drum and continuous light halogen light bulb. Modern ones use pulsed xenon at particular wavelength settings. The industrial versions read considerable more points than paint store versions, and hence get a more accurate reading due to less interpolation. But X-Rite has developed devices of this nature up to millions of dollars in cost for special applications. The bigger problem is at the operator end. Paint matching machines a like a round of golf - they save labor getting the ball onto the green, but never achieve hole in one. Just try getting an accurate off-white match. A trained pro eye has to actually make the final gentle hits of the ball into the hole. The machines themselves operate on a computerized 4-axis analytic geometry program based on CIE color mapping, just like inkjet printers do.
I dealt in top-end Euro clear and translucent finishes, especiallyh or the marine variety, but not paints. But even in the best brands, no good painter imagines there will be an identical match liter to liter, or even gallon to gallon. They always want enough to cover at least a full wall at a time, so that no discrepancy will be evident.
Auto paint matchers are the best; but we quit hiring them because most of them had many years exposure to nasty solvent fumes like toluene, much like glue-sniffers, and sometimes went berserk right on the job. Now there's a turn to safer automotive acrylics. In terms of architectural paints, you have to hunt down serious paint stores with real pro clientele and high-quality brands like Benjamin Moore, and see if anyone on site has serious matching skills. Some might charge dearly for the service, other reasonably ask you to leave you sample so they can take their time doing it correctly. Even the paint factories and R&D labs have highly trained personnel who do the tweaks and evaluations mostly by eye, and only partially by machine. They make seriously good money too. Whether under those circumstances or in a color darkroom, learning how to look at things, what to compare, is just as important as the physiological aspect of normal color vision. When I trained color matchers, it started with basic art school color theory - basic principles like simultaneous contrast, successive contrast, metamerism, etc. We would have hired Van Gogh in an instant, since he wasn't making any money selling his paintings anyway.
When I did color consulting on the side, I'd charge $100 an hour plus travel expenses; and that was back in the 80's. Now it would be double if I still had time and energy for it. Plus the same architects would hire me to do the 4X5 camera project shoots and make their portfolios, and sometimes buy framed personal prints from me too. So it was a decent gig when I was still young enough to basically juggle three jobs at the same time. At that time there were only two other people in NorCal all providing that service, and I got much of my business from dissatisfied clients one of them. There's an awful lot that goes into it - visiting the site during representative times of the day, evaluating surrounding enviro colors and the psychological and physiological effects of adjacent colors and seasons, how the paint colors will differentially age over time with respect to each other and planned repainting cycles. I once had a famous gourmet chef ask me to match the color of the trim on his restaurant to the color of his wine bottle labels. I was the only one in the whole region who knew how to do it. That kind of thing would fry the brains of any paint match machine. I should know. When I stated I was a guinea pig for the development of those devices, they'd deliberately seek me out to find the flaws in their system. One of them was the head of the International Color Council, who had a seven figure annual income. We understood each other; even though I was only a little flea compared to his pay grade.
Now per Kodak versus MacBeth. Color control was the primary business of McBeth. They offered color matching booths, special matching light tubes, color densitometers, reference charts, etc. Kodak did sell special density reference plaques for calibrating instrumentation; but the difference between those and a printed gray card is like the distinction between a pile of ten buck Kodak branded thermometers laying on a camera store shelf and their certified scientific grade ones costing two or three hundred dollars apiece. The quality control standards are drastically different.
But just like darkroom thermometers, what counts in a gray reference is repeat predictability. If your cereal box cardboard is what you are accustomed to, and know how to tweak exposures in reference to, along with your own particular meter, that's fine. But cardboard isn't inert; and it's certainly not appropriate for analytical work.
And yes, it's a fascinating topic. Glad you are interested in it too.
