Apple Color 1.5 - Manual (Page 228)

To prevent obvious banding or other artifacts, adjustments to the three tonal zones
overlap broadly, with each color balance control's influence over the image diminishing
gradually at the edges of each zone. This overlap is shown in the following graph.
Shadow control influence
Midtone influence
Highlight control influence
The ways in which these zones overlap are based on the OpenCDL standard, and their
behavior is described below.
Important: If you're used to the way the Color Corrector 3-way filter works in Final Cut Pro,
you'll want to take some time to get used to the controls of the Primary In room, as they
respond somewhat differently. Also, unlike adjustments using the Color Corrector 3-way
filter in Final Cut Pro, adjustments made using the color balance control affect the luma
of the image, altering its contrast ratio.
228 Chapter 9 The Primary In Room