Wheee! I said I'd post this when I finally had one success, and my last string of test results came out a match, so, folks, here's the Mad Scientist with some details on the latest experiment.
I'm trying to match skin tones for dolls with acrylic paints, just for those times when it might be necessary to paint part of a doll to cover a stain, to cover sculpt modifications done with all-purpose caulk, or just because I have to paint a head to actually have it match a body.
My first test subject was a Palm Beach Always Dressed Barbie, with the purple painted on bathing suit. This matches the skin tone of the blond Fashionista Barbie in the purple dress, and possibly also other Barbies I am not sure of, as I am no expert in Barbies.
I thin my paints down a lot, but I keep them very carefully the same ratio of paint to water-and-Liquitex-Flow-Aid so that my pigment proportions are consistent and reproducible. After all, an experiment is worthless if you can't reproduce your results. I keep the pre-thinned paints in dropper bottles so I can mix them by the drop for small test batches. I use Liquitex Basics acrylic paints.
One issue is that the red pigments want to air-dry a little faster than the yellow ones and this could cause streaking or color variations in your work. I advise dabbing the paint on with a sponge and then drying with a hair dryer held far enough from the doll not to cause the paint to make runs or drips. Drying the paint faster in this way prevents any pigment separation.
Based on tests, and checked under several different kinds of lighting including full sun, the paint match for Palm Beach Always Dressed Barbie in purple bathing suit and other dolls of the same skin tone is:
6 Parts Cadmium Yellow Light
5 Parts Red Oxide
8 Parts Titanium White
1 Part Neutral Grey 5
Here's an example test on the doll leg. Most of the area below the seam is not painted. Above the seam is. At one point near the middle you can see some brushstrokes/paint edge. In the upper right you might barely make out some of the color separation I mentioned, in this case caused by drips because I had the hair dryer too close.
... now I have to decide whether my next test subject will be Fleshtone Obitsu or pale-variant LIV Alexis... At least I can now finish Alya's faceup as I've successfully painted over the caulk used to remove the Barbie-Grin from her headsculpt.
Alya before, with a non-matching paint over the acrylic latex caulk work.
Alya now, after area around mouth painted with matching paint.
Anyone else ever do this, or want to try to beat me to a match? XD