Apple Color 1.5 - Manual (Page 231)

This lets you make color adjustments that exclude the shadows and highlights in the
image. For example, you could add a bit of blue to the midtones to cool off an actor's
skin tone, while leaving your shadows deep and untinted and your highlights clean and
pure.
Highlights Color Adjustments
Adjustments made using the Highlight color balance control apply a multiply operation
to the image—the color that's selected in the Highlight color control is simply multiplied
with that of every pixel in the image. By definition, multiply color correction operations
fall off in the darker portions of an image and have no effect whatsoever in regions of 0
percent black.
231 Chapter 9 The Primary In Room