Apple Final Cut Pro 7 - Manual (Page 1372)

Color balance controls are color wheels that allow you to change the mix of red, green,
and blue that falls within the area of a specific range of luma in your clip. The color balance
controls act like virtual trackballs; you can drag anywhere within a color wheel to move
the color balance indicator. The Color Corrector 3-way filter has three color balance
controls: one affects the blacks of a clip, the second affects the midtones, and the third
affects the whites.
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
1372 Chapter 81 Color Correction Filters