lightness
HSLColor structure
#include <Picker.h>
typedef struct HSLColor { Size Offset Description
SmallFract hue; 2 0 Fraction of circle, red at 0
SmallFract saturation; 2 2 0-1, 0 for gray, 1 for pure color
SmallFract lightness; 2 4 0-1, 0 for black, 1 for white

Notes: For developmental simplicity in switching between the HLS and
HSVmodels, HLS is re ordered into HSL. Thus both models start with hue and
saturation values; value/lightness/brightness is last.