I feel very uneasy about the CMYK&RGB ratios being “solutions” for skin tones. Not only in the sense of “i’m colorblind and need an aid in nailing proper colors” but also in general sense of it not being a solution at all.
First - CMYK & RGB - CMYK color model - Wikipedia - look at Conversion section and first thing that pops is “CMYK and RGB are device dependent and there is no general conversion formula between them”. Even worse is trying to adapt generic formula that “sorta works” based on some video with no related proof of ow it should “work” (eg scientific article, or even something other than gut feeling how skin looks)
Second - there’s not one “skin tone” nor even for “lighter” skin tones. if you were to apply this even as a starting point to portrait of me and my brother we’d look “off” (either one or another) since we do differ. If you were to shot male and female of same ancestry and age (say twins), you’d get similar thing. If one person were closer to light source than another - same thing. Oh… Light source!
3rd - light source, reflections, balance… light messes everything up 
or rather - light centric approach here would be a tad bit closer to reality but then
then there’s problem of getting “style” - you now “color grading”? Like in some movies some scenes are greenish, some are blueish, some are warm, some are cold… It all depends on mood (or chromatic adaptation) and this would fall apart in all situations like those.
So with goal being of getting “skin tones right” (stepping aside problem of being color blind), the steps should be same as for any color grading: relicate shot conditions and compensate for variations (think white balance etc), compensate for viewing intention (tbh showing picture on bright bg differs from showing on dim bg), optimize appearance of elements you want to show (think make subject “pop”), do the desired effect/mood/look of a scene.