What is it that you want to appear in the table?
Since "pm3d" is a coloring algorithm, it's not clear to me how you
could put a pm3d plot in a table other than to store the original points
and the coloring scheme.
But you can do that already, by saying something like
set table "data.tab"
splot FOO
set print "color.dat"
show palette palette 256
unset table
unset print