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One of the limitations of the new device I've been using is that it constrains its output to a range ~25-95 Agtron gourmet scale, but one of the first significant events in coffee roasting involves that measurement going off the scale (my benchtop analyzer would put it around 130). Decaf coffees, however, often start out brown so they reach their brightest at a reading that's still in range. That inflection from coffee getting brighter to coffee getting darker is where tasteable chemistry starts
Since the device generating those readings is already doing a conversion to L*a*b* and I have the ability to modify its source code, I'm tempted to add another label to the display to see if the a* reading reliably tracks the transition from green to yellow on coffees that haven't been decaffeinated (or if I can do something to make it track).