It would conceptually work as follows :
- Consider the bins selected in the histogram
- The center of gravity (CoG) of the histogram measurements in selected bin defines the average hue-saturation of the selection
- A vector from the CoG to the image's local color measures the color difference between the CoG and the Hue-Sat of the input image
- Controls, such as sliders, could independently adjust the image's HSV or HSL components to magnify or attenuate the difference