color_assignment

The default pm3d coloring assigns an individual color to each quadrangle of the surface grid. For alternative coloring schemes that assign uniform color to the entire surface, see pm3d fillcolor.

A single gray/color value (i.e. not a gradient) is assigned to each quadrangle. This value is calculated from the z-coordinates the four quadrangle corners according to corners2color <option>. The value is then used to select a color from the current palette. See set palette. It is not possible to change palettes inside a single splot command.

If a fourth column of data is provided, the coloring of individual quadrangles works as above except that the color value is distinct from the z value. As a separate coloring option, the fourth data column may provide instead an RGB color. See rgbcolor variable. In this case the plotting command must be

      splot ... using 1:2:3:4 with pm3d lc rgb variable

Notice that ranges of z-values and color-values for surfaces are adjustable independently by set zrange, set cbrange, set log z, set log cb, etc.