Principal compression and tension stress and strain plots

Hi,

I have a question with regards to the various stress-strain plots that I see from FEM softwares.

They have plotted principal compression and tension stress plots  and strain plots for a 2d geomterical analysis from a FE software (MARC). They have used a finite strain theory. So does this mean that the principal compression and tension values for the various elements just correspond to the minimum and maximum values of a Cauchy green tensor or some other finite tensor like first or second piola kirchoff stress tensor??