Is matching the color of a pinched cheek or pinched finger a good way to pick your lippy and blush colors?
Well, the answer is a little complicated.
The color of your pinched skin is usually the effect you're going for. That's true.
But you won't achieve that effect by matching that color and then putting it on your skin.
When you pinch your cheek or finger, you're seeing a color that combines the red of your blood with the brown of your skin tone. (All human skin is some variation of brown.)
This is why your pinched-skin color is less saturated than the actual reds and pinks in your swatches. (Try it and you'll see.)
If you choose a red or pink that you've matched to a pinched finger, it's already desaturated, because it's a combination of your body's red with your skin. As this matched color mixes with your skin color, it gets further desaturated -- most likely too desaturated for you.
So, to create that same pinched-skin effect on your skin from the outside, you need to add a purer, less browned red or pink to the brownish tone of your skin.
This is where your swatch reds and pinks come in.
When you apply a purer red or pink from your swatches to your skin, the result that the viewer sees is a color that combines that red or pink with your skin. So the color you end up with is very similar to the pinched-skin color.
That's the effect you're going for. It's a less saturated version of the pure swatch red or pink because it's blended with your skin color, and it looks perfect on your skin.
That's how your palette reds and pinks are supposed to function. They shouldn't sit on top of your skin like red circles of blush on a Raggedy Ann doll, right?
This is the same reason that matching makeup colors to your palette by swatching them on your skin is wrong, wrong, wrong. For purposes of matching your palette, makeup should only be swatched on white paper.
If you "swatch" makeup on your skin, you're not learning what color it really is; you're learning what color it looks like mixed with your skin color.
That information is interesting information. But it's not the information you need in order to know whether a pink or red matches your actual palette colors. You're looking to match those reds and pinks.