If non zero, force the color scale to use the COLOR SHOW_COLOR command automatically in order to have a Look-Up-Table that is white (or black if SHOW_COLOR is negative) around 0 to visually attenuate the contrast around the noise level.
SHOW_COLOR value is interpreted according to the last specified /TYPE option of command COLOR, i.e. eithre in Hue range (0 to 360) or in noise units.