Color Theory and Polymer Clay
Polymer Clay is pigment based and follows the same "rules" as all pigment based color theory and color mixing.
https://99designs.com/blog/tips/the-7-step-guide-to-understanding-color-theory/
https://www.canva.com/colors/color-wheel/
https://mymodernmet.com/basic-color-theory/
https://blog.psprint.com/printing/134/
Make a Palette:
From a photo:
https://www.canva.com/colors/color-palette-generator/
more complex:
https://paletton.com/#uid=1000u0kllllaFw0g0qFqFg0w0aF
Use an App:
https://www.polymerclayer.com/colormixr.html