Zorn is known to use a basic color palette consisting of Lead White (Flake White), Yellow Ochre, Vermilion and Ivory Black. This limited color palette shows tremendous range in terms of color mixing.

A large variety of tonal ranges are possible to mix and considered as a very important development for portrait painting. However, the color palette can also be used in still life and landscape painting under certain circumstances.

Zorn’s Palette Peculiarities

Most striking aspect is that a kind of an olive green color is possible to obtain by mixing Ivory Black and Yellow Ochre as Ivory Black is bluish in nature.

However, the notion that Zorn used only these four colors is untrue. His paintings show the use of other auxiliary colors wherever needed. Source: Wikipedia.