The mid-tone grey paper palette I mentioned is called Grey Matters and is sold at Amazon as well as many art stores.
As for questions about skin tone-- The shadow color was made from burnt sienna, (with just a touch of ultramarine blue and white). The clean peachy color in the last portrait was a Stephen Early suggestion, using cadmium green pale + scarlett cadmium + white. Some other great skin tone combos to try are Carolyn Anderson's use of "a purple" (like dioxazine) + yellow ochre and white. Another is viridian green and cad orange, plus a tiny amount of cadmium red light and white.
Also, Kim English sometimes uses purple and orange to make a beautiful rich brown that can be tweaked warmer or cooler for a great skin tone in shadow or light (with white). And then it is also fun to experiment with any combination of reds and yellows + white; warm and cool reds (like cad red light and alizarin) plus warm and cool yellows (like cad yellow med., cad yellow pale or lemon yellow)--And sometimes a pinker version is best, so I go with permanent rose or quinacridone, plus a yellow. And in all these examples, you can always add in a little modifier like green if the color is too warm...And there are lots of others, plus you can get lovely skin tones using a simple limited palette of red, yellow and blue. The key is to observe the model and paint what you see, but sometimes trying new combinations like the ones above make it easier to "find" what you see. At least that is true in my case...But, having said all that, seeing and capturing the overall skin tone is One Thing--then there is the ability to capture the nuances of color within the lights and shadows-- now THAT is truly something I know very little about, but am thrilled to learn. The absolute best example of what I am talking about is Robin Frey's figures and portraits--take a look at this stunning portrait to see what I mean-(as well as the other extraordinary examples on his website).
Now THAT is the best kind of chi!
"Colors are brighter when the mind is open"...Adriana Alarcon