Apple Color 1.0 - Manual (Page 188)

188 Chapter 9 Primary In
 Adjustments made to the midtones affect the broadest area of the image, but don’t
affect the lowest percentages of the shadows or the highest percentages of the
highlights.
 Adjustments made to the highlights affect the midtones as well, but not the lowest
percentages of the shadows.
Controlling Color Balance Control Overlap
While the tonal zones that are affected by the three color balance controls are
predefined by the mathematical operations they perform, it is possible to exert some
control over what areas of an image are being affected by the corrections of a
particular color balance control. This is done by applying opposing corrections with
other color balance controls.
The following example shows this principal in action. If you adjust the Highlight color
balance control to add blue to a linear gradient, you’ll see the following preview.
As you can see, this change affects both the whites and midtones. If you want to
restrict the correction that’s taking place in the midtones, while leaving the correction
at the upper portion of the whites, you can take advantage of the previously described
method of using complementary colors to neutralize one another, and make a less
extreme, opposite adjustment with the Midtone color balance control.