Apple Color 1.5 - Manual (Page 281)

The secondary curves use B-Splines, just like the primary curves controls. In fact, you add
and edit control points on the secondary curves in exactly the same way. For more
information, see
Curve Editing Control Points and B-Splines .
Important: Adjustments made using the secondary curves cannot be limited using the
vignette or HSL controls.
Using the Secondary Curves
This section provides examples of how to use each of the three kinds of secondary curves.
Important: Curves cannot be animated with keyframes, although just about every other
parameter in the Secondaries room can be.
The Hue Curve Tab
When you raise or lower part of the secondary Hue curve, you make a hue adjustment
similar to the one you make when you use the Global Hue control, except that you only
rotate the hue value for the selected range of hue specified by the curve. Raising the
curve shifts the values toward red, while lowering the curve shifts the values toward blue.
Before
Hue curve adjustment
After
This control can be valuable for making narrow, shallow adjustments to the reddish/orange
section of the spectrum that affects skin tones, in order to quickly and smoothly add or
remove warmth.
281 Chapter 10 The Secondaries Room