If you use the eyedropper to select the color to be keyed out in the overlay track clip, and Similarity to give a wider range of color to be keyed if required, you should end up with the green (or whatever) colors disappearing and thus showing though to whatever you have on the tracks below.
If you have a central subject and the keying is less than perfect further out, you can use one of the garbage mattes to restrict the overlay to areas where keying is good (if any!).
If you have done all this and the key is inverted (which it should not be), you can then apply the Alpha Adjust effect and select the Invert Alpha option to reverse the effect.
If this doesn't address the question you are hinting at, please explain much more fully what you have done and what the result has been.