I had the same question, so I opened up the clips, set up the node tree, and started playing. At first it appears to be somewhat magical, but it suddenly makes sense with an RGB waveform monitor (or an RGB parade scope) and a vectorscope. What I noticed is that when the Red output is fed also by the Blue channel, the vector scope show everything being pulled and stretched toward the R target. When the Green output is fed also by the Blue channel, the red-stretched blob rotates and stretches toward the Yl target. You can then watch the magic happen as you rase the Green output into the Blue Channel. What was a large outstretched limb of color pointing towards Yl squishes very quickly to a very thin line that points between R and Cy. Those two complementary colors provide a credible balanced look that simply has no other colors to it--no Mg, no B, no G, and no Yl. But that narrow balanced line is not aligned with the skin-tone line. This can be fixed by rotating the Hue, or by subtracting Red output and re-adjusting Green output to get back to the thin wispy line. When the remaining colors are aligned with the skin tone line, the skin tones look natural, and the balancing complementary colors on the other side of the center make the look. I got this with the following
Red Channel: 1 R + 0.9B
Green Channel: 1 G + 0.9B
Blue Channel: 0.91 G + 1B
Hue Rotation: 43.4
Without Hue rotation I got the lines to line up with Blue = -0.5 R + 1.41 G + 1B
When I raised the Green output to 2.0 I needed to drop Red to -1.07 and I observed the need for a Hue rotation of 53.30 to get back to the skin-tone line. I also noticed that using larger numbers in the Blue output channel results in greater saturation, which may or may not be desirable.
But I think that the fundamental operation we see here is using the RGB Mixer to take us from 3 colors to 2 while letting the skin tone be the skin tone.
I will also say that it is INVALUABLE to have a Resolve Mini panel with which to be able to twiddle two knobs that send the colors in opposite directions so that one can maintain the target of the skin tone line while seeing how all the other colors react to various parametric alternatives!