I love mixing my own skin tones and you will get better as you go along. Just have confidence in yourself. Just keep mixing and experimenting and have fun. I use 3 main colors for my base skin tone colors in the Liquitex soft body. Sandalwood for light skin, taupe for medium skin and add burnt umber to the taupe for darker skin tones. You can add small amounts of other colors such as red to add a rosy tone, yellow oxide for caramel tone and burnt sienna for a more bronze tone, to name a few. Just mix until you are happy. I don't measure or have recipes. I eyeball it until I get the color and tone that I want and like. I hope this helps.
Here is an example of a Shyann that I did in which I wanted her to have a soft pale skin tone. I used the sandalwood and added some taupe to darker it just a bit.
Here is Greta Marx that I did with using taupe and adding burnt umber for a darker skin tone.