Use the Colour Curves node to adjust the colour in the front, back, or key-in clip. For example, increase or decrease a colour in an image by plotting the colour and adjusting the curve. When you move the first or last keyframe, the other keyframes move by the same amount so that curves are continued from beginning to end.
You can add Colour Curves nodes to any part of the pipeline except to the Front and Matte pipes of MBlend nodes and the Matte pipes of CBlend nodes. This is because these pipes are designed to produce a matte, and the result of the Colour Curves node is a colour image.
Colour Correcting the Result Clip.
The Colour Curves menu is identical to the Colour menu in the traditional Keyer. See