Secondary Color Correction Primer - The Art and Technique of Digital Color Correction - page 163

rarely use secondary color correction for such obvious chores. Instead,
secondaries are used subtly for much more natural corrections. Some
of the main targets for secondary color corrections are skin tones, sky,
water, and grass.
Primary color correction often must be done with an eye on the
big picture and an understanding that the goal is to make most of the
image look good but also that certain things, like skin tones, may
need additional work with secondaries. As you may have noticed, the
items I mentioned in the previous paragraph—skin, sky, water, and
grass—are all things that people have a natural understanding about
and preconceived notions regarding what colors these things should
be. Often, getting a primary color correction to look good across most
of the image will take these specific items out of the color range that
most people are expecting. Sometimes, if you want to warm up an
entire image, the skin tones will go much too orange. Or, by pulling
the unwanted blue cast out of an outdoor scene, the grass will turn
yellowish. Or, by bringing up the levels of the foreground elements of
the picture, the sky will become overexposed. All of these things call
for a secondary color correction that isolates or qualifies the problem
area and fixes just that portion while leaving the rest of the primary
correction alone.
Secondary color correction is often used to fix the things that the col-
orist “broke” in the primary correction. For example, in trying to match
the colors and luminance values of two shots, a colorist may use primary
color correction to get the majority of the shot to match, but will find that
the only way to do that is to have the sky of one shot be a strange color. In
this case, the colorist would match most of the shot using primaries, then
use secondaries to fix the problem with the sky. This situation often hap-
pens with images that have a color cast in addition to clipping, because
the clipping in the dominant color cast will cause any corrections to the
unclipped portions of the image to deliver some very strange colors to the
clipped areas.
Secondaries are also often used to make the subject of the shot “pop”
or to focus the viewer's attention on something important. This task is
often done with a vignette, which slightly darkens the edges of the image
and points the viewer's eyes to the main focus of the shot. It can also be
done by qualifying an important part of the image and increasing the
saturation or contrast in that portion of the image to draw the viewer's
attention to it.
Many colorists I spoke with love getting into specific parts of the pic-
ture to work in isolation on that area, but not everyone is in complete
agreement about the technique.