How do I CC keyed actor without affecting BG?

I've keyed out an actor over a background. I added a Color Corrector node to the stream before the background Merge, but the CC still affects the whole image. How can I CC the actor alone?

Thanks in advance.

This is related to what CC actually does to pixel values. Some operations, like lift, offset etc can move the black level or change relation of RGB and alpha values. When image is merged over BG, these pixels change the color of background through additive blending.

Consider the equation for over operation:
C = A*alpha + B*(1-alpha)

Here C is the result, A is foreground, B is background and alpha is foreground transparency. Basically it is just a linear interpolation based on alpha factor. To speed things up, A*alpha operation is usually done beforehand. This is called premultiplication. Merge operations like over expect this to be done and for equation to work, RGB channels must have value zero where alpha is zero. But if you lift the black level, these nonzero pixels contaminate the background.

To get past this problem you must remove premultiplication before CC and reintroduce it after. Either add Alpha Divide before CC and Alpha Multiply after CC to do it explicitly or just check the pre-divide/post-multiply checkbox in your color correction node settings. If you are using separate alpha process, simply do your CC before copying and premulting with alpha.

Thanks, Hendrik.

What I ended up doing was attaching the Delta Keyer's output to a Channel Boolean as a separate branch. This gave me the alpha. Then I added a CC in the main stream, connected the output of the Boolean as an Effect Mask to the CC node. I don't know if that's a common approach, but it worked. I forgot about the "pre-divide/post-multiply checkbox" is in the CC node. I'll try that next time.

Do you know of any in depth tutorial that explains compositing with keying for Fusion? I own both DaVinci Resolve Studio 15 and Fusion 9 Studio. Any walkthrough that explains how best to composite green screen elements would be awesome.

The most in-depth free series on keying by far is the Advanced Keying Breakdown series by Tony Lyons. It takes a lot of time to explain the "why", not just "how". It is based on Nuke, but logic is the same everywhere, Fusion, Natron, AE etc. You can get to start from this link, just look for all videos from his channel to get whole series:

Thanks, Hendrik. I'll look up more on Tony Lyons and see what I can glean from his tutorials.

The task is to find/figure out what nodes in Nuke have a Fusion equivalent. I'm still new to Fusion, so I don't have the intuition that many longtime users of Fusion have. There are tons of tutorials for people moving from After Effects to Nuke. I don't know what tutorials there are of Nuke to Fusion.

Over time I'll get more acquainted with Fusion.