After asking about Foundry paints for Indian skin tones, I did a bit of web research and number-crunching. This seemed to be the best existing thread to post my quick findings.
I found a website that had the apparent RGB values of the first 50 or so Foundry paint triads:
http://www.danbecker.info/minis/miniother/PaintCharts/index.htmlNext, after some data cleansing and transformation, I calculated the matrix of their weighted colour distances, and checked for distances below 100 units. Some apparent proximities were rather odd in light of the colour chart, but most made sense.
What it tended to confirm for the flesh-, tan-like, and brownish triads is that only very few are internally coherent, where the three colours in a triad are close to one another. Often, the shade and mid tones are close enough, but the highlight is far off. Some colours match better outside of their own triads. Surprisingly, at least one pair of differently-named colours seems to coincide according to the distance measure!
Long story short, it would seem that one cannot always rely on Foundry's chosen triads to select base, mid, and highlight colours that match well.