Apple Color 1.5 - Manual (Page 261)

The state of the Enabled button is also keyframable. This means you can use keyframes
to control this button to turn a secondary effect on and off as the shot plays. For more
information on keyframing, see
Keyframing Secondary Corrections .
Choosing a Region to Correct Using the HSL Qualifiers
One of the most common ways of isolating a feature for targeted correction is to use the
HSL qualifiers (so named because they qualify part of the image for correction) to key on
the portion you want to color correct. HSL stands for hue, saturation, and lightness, which
are the three properties of color that together define the entire range of color that can
be represented digitally.
HSL qualification is often one of the fastest ways to isolate irregularly shaped subjects,
or subjects that are moving around in the frame. However, as with any chroma or luma
key, the subject you’re trying to isolate should have a color or level of brightness that’s
distinct from the surrounding image. Fortunately, this is not unusual, and reddish skin
tones, blue skies, richly saturated clothing or objects, and pools of highlights and shadows
are often ideal subjects for secondary correction.
If you’re familiar with the Limit Effect controls of the Color Corrector 3-way filter in
Final Cut Pro, you’ll find that the Secondaries room HSL controls work more or less the
same way.
261 Chapter 10 The Secondaries Room