Apple Color 1.5 - Manual (Page 243)

To make a targeted color cast correction
1 Add a control point to the red curve near the bottom of the curve, and pull down until
the red color cast becomes subdued.
This should coincide with the bottom of the red waveform in the Parade scope lining up
with the bottoms of the green and blue waveforms.
This operation certainly neutralizes the red in the shadows; unfortunately, because this
one control point is influencing the entire curve, the correction also removes much of
the original red from the midtones as well.
Tip: If you're wondering where you should place control points on a curve to make an
alteration to a specific area of the image, you can use the height of the corresponding
graphs in the Waveform Monitor set to either Parade (if you're adjusting color) or Luma
(if you're adjusting the Luma curve). For example, if you want to adjust the highlights of
the image, you'll probably need to place a control point in the curve at approximately
the same height at which the highlights appear in the Waveform graph.
243 Chapter 9 The Primary In Room