Scaleable Density Palette Schema uses traffic light colors. Use -scalePal together with a scalar factor in opalsZcolor to specify the reference density REF (e.g., the expected density). Values from 1.0*REF onwards are color-coded in different tones of green. The more the density increases the darker the green (= decrease of lightness). Values between 0.75*REF and 1.0*REF appear in yellow. Values between 0.5*REF and 0.75*REF appear in orange. Below 0.5*REF the values appear in red. Alternatively, the median of the point density can be used as REF. This way the full color range is exploited for representing the density distribution. Hint on rows in palette definition: all values within [this_val, next_larger_val) get this_color