Yeah, thatīs cool thing "Bruce Beard's Hair & Skin Color Charts". But currently I just use an aditional Photoshop filter "PhotoTune.SkinTune.v2.0"
And obviously my "memory colorīs" values

In general caucasian humanīs skin have 3/4 of cyan, from magentaīs values. And the yellow could be a little bit highter than magenta. And zero of black. The sample pointīs area could be chosed out of shadows and make-up influence. Something like C:7 M:23 Y:26 K:0
Obviously thatīs not a law. Photos may have a heck of a lot of conditions. But thatīs what i have in my mind like a reference

good luck.