Keying - Nuke 101: Professional Compositing and Visual Effects - page 330

HueCorrect has several functions, all of them having to do with selecting a hue
and moving a point on the graph. The curves you can manipulate include satur-
ation, luminance, red, green, blue, red suppression, green suppression, and blue
suppression. The difference between changing green and suppressing green is
that changing simply multiplies the amount of green, and suppressing reduces the
amount of green so that it's not higher than that of the other two channels.
To reduce the amount of green in the brown color of her hair and face, you first
need to find out where that color is in the graph. This works in a similar way to
the HueKeyer node.
2. While viewing the RGB channels of HueCorrect1 in the Viewer, hover your
mouse pointer around the hair and face areas.
The resulting yellow line in the graph shows a hue at around 1.5. This is the area
where you need to suppress green. To suppress the green color, you will use the
G_sup curve in the Curves List window on the left.
3. Click G_sup in the Curves List window.