Gnuplot/color

Color specification
 * explicit rgb (red, green, blue) values
 * hex-string (like "#0000ff")
 * rgbvalue (like "256")
 * named colors
 * color values that refer to the current PM3D palette
 * palette cb -45    # whatever color corresponds to -45 in the current cbrange of the palette
 * palette frac 0.3  # fractional value along the palette