An implementation of the hue-saturation colour model in which the luminance is defined as the average of the highest and lowest RGB values. This approach takes more properties of the underlying colour into account than the HSV space, but by no means provides a perceptually constant luminance cross section for any given value. That is, blue hues tend to look much darker than yellow hues despite having the same L value. The Grasshopper colour picker does not provide access to the HSL space.