Apple Color 1.5 - Manual (Page 247)

Beware of raising image saturation too much; this can result in colors that start to
"bleed" into one another and a signal that's illegal for broadcast.
A dramatically oversaturated image
If the Broadcast Safe settings are turned on, the legality of the image will be protected,
but you may see some flattening in particularly colorful parts of the image that results
from the chroma of the image being limited at the specified value. You can see this in
the Vectorscope by the bunching up at the edges of the graph. Even if you're not
working on a project for video, severely oversaturated colors can cause problems and
look unprofessional.
• Highlight Sat.: This parameter controls the saturation in the highlights of your image.
You can selectively desaturate the highlights of your image, which can help legalize
problem clips, as well as restore some white to the brightest highlights in an image.
Highlight saturation turned all the way down
Highlight saturation turned up
247 Chapter 9 The Primary In Room