Apple Color 1.0 - Manual (Page 200)

200 Chapter 9 Primary In
Since the key light for this shot is the sun coming in through the window, this is
probably inappropriate and should be corrected.
3 Drag the control point for the white point in the red curve control down until the red in
the brightest highlights of the face is neutralized, but not so far that the lighting begins
to turn cyan.
At this point, the correction is finished. The red light appears in the fill light falling on
the woman’s face, while the shadows and very brightest highlights from the sun are
nice and neutral, enhancing the color contrast of the image.
Here is a before and after comparison so you can see the difference.