If you want to build a palette using only natural or earth pigments here are some available options. A palette like this could be used for any application including portrait and landscape, but it would be impossible to achieve certain chromas.
Any ochre
Any sienna
Any umber
Any earth
Caput mortem violet
Any white
Any black
Davys grey
English/Persian/Indian/Venetian Red
Terre vert
Ultramarine blue
VanDyke brown
Any Mars
