Apple Final Cut Pro 7 - Manual (Page 1359)

The angle of distribution of red, green, and blue in all the color balance controls
corresponds to the angles of those colors in the Vectorscope. The direction in which you
move the color balance indicator within the color wheel is matched by the mix of colors
moving in the same direction in the Vectorscope.
If you hold down the Shift key while dragging a color balance indicator, the angle of the
indicator is constrained, so that the indicator can only move out toward the edge of the
color wheel, or in toward the center. This lets you change the intensity of your color mix
without changing the distribution of hues.
Color balance indicator
path constrained by the
Shift key
Unlike other controls in Final Cut Pro, a color balance control doesn’t “gear down” when
you hold down the Command key while manipulating the color balance indicator (allowing
you to make more subtle adjustments); rather, it “gears up” the control, causing the
indicator to respond more quickly and resulting in greater changes.
Note: The Color Corrector filter is more likely to be supported by real-time hardware than
the Color Corrector 3-way filter.
1359 Chapter 81 Color Correction Filters