The saturation of a color is the distance of that color from a
gray of equal intensity.[18] Haeberli has suggested
modifying saturation using the equation:
where:
with 
, 
, and 
as described in the above section. Since
the saturation of a color is the difference between the color and a
gray value of equal intensity, it is comforting to note that setting
s to 0 gives the luminance equation. Setting s to 1 leaves
the saturation unchanged; setting it to -1 takes the complement of
the colors [26].