Apple Color 1.5 - Manual (Page 280)

For example, if you add four control points to the Saturation curve to lower the
green-through-blue range of the curve, you can smoothly desaturate everything that’s
blue and green throughout the frame, while leaving all other colors intact.
Before After
Sat curve adjustment
One of the nicest aspects of these controls is that they allow for extremely specific
adjustments to narrow or wide areas of color, with exceptionally smooth transitions from
the corrected to the uncorrected areas of the image. In many instances, the results may
be smoother than might be achievable with the HSL qualifiers.
Another key advantage these controls have over the HSL qualifiers is that you can make
simultaneous adjustments to noncontiguous ranges of hue. In other words, you can boost
or lower values in the red, green, and blue areas of an image while minimizing the effect
of this adjustment on the yellow, cyan, and magenta portions of the image.
280 Chapter 10 The Secondaries Room