Apple Color 1.5 - Manual (Page 222)

Contrast Affects Color Balance Control Operation
There's another reason to expand or otherwise adjust the contrast ratio of an image before
making any other color corrections. Every adjustment you make to the contrast of an
image changes which portions of that image fall into which of the three overlapping
tonal zones the color balance controls affect (covered in
Using Color Balance Controls ).
For example, if you have a low-contrast image with few shadows, and you make an
adjustment with the Shadow color balance control, the resulting correction will be small,
as you can see in the following gradient.
If, afterward, you adjust the Shadow or Midtone contrast sliders to lower the shadows,
you'll find more of the image becoming affected by the same color correction, despite
the fact that you've made no further changes to that color control.
This is not to say that you shouldn't readjust contrast after making other color corrections,
but you should keep these interactions in mind when you do so.
Color Casts Explained
A color cast is an unwanted tint in the image due to the lighting, the white balance of
the video camera, or the type of film stock used given the lighting conditions during the
shoot. Color casts exist because one or more color channels is inappropriately strong or
weak. Furthermore, color casts aren't usually uniform across an entire image. Often, color
casts are stronger in one portion of the image (such as the highlights) and weaker or
nonexistent in others (the shadows, for example).
222 Chapter 9 The Primary In Room