with pm3d (pm3d explicit)

Syntax

     splot DATA using (x):(y):(z){:(color)} with pm3d
                {fs|fillstyle <fillstyle>} {fc|fillcolor <colorspec>}
                {zclip [zmin:zmax]}

The rendering properties of all pm3d surfaces are controlled using set pm3d. By default the full surface is rendered as a grid of quadrangles, each colored by the palette color mapped to that z coordinate. If you provide a fourth input column, the palette mapping uses that value rather than z. See pm3d fillcolor, pm3d color_assignment.

When you explicitly use with pm3d in the plot command rather than using another plot style while set pm3 implicit is active, additional rendering options are possible. This allows you to use separate coloring schemes for different surfaces in the same plot.

EXPERIMENTAL: This gnuplot version introduces an option zclip that clips the generated surface smoothly at a pair of limiting z values. The example below animates gradual removal of the top portion of a two-color 3D surface.

     set style line 101 lc "gray"
     set style line 102 lc "blue"
     set pm3d depthorder
     do for [i=0:N] {
         splot f(x,y) with pm3d fillcolor ls 101 zclip [* : zmax-(i*delta)] 
         pause 0.2  # 1/5 second between animation frames
     }