By default the colors assigned to pm3d objects are not dependent on orientation
or viewing angle. This state corresponds to set pm3d nolighting.
The command set pm3d lighting selects a simple lighting model consisting of a
single fixed source of illumination contributing 50% of the overall lighting.
The strength of this light relative to the ambient illumination can be adjusted
by set pm3d lighting primary
fraction
. Inclusion of specular highlighting
can be adjusted by setting a fractional contribution:
set pm3d lighting primary 0.50 specular 0.0 # no highlights
set pm3d lighting primary 0.50 specular 0.6 # strong highlights