After I chroma key, if I add other effects, the chroma key is negated and the green screen is shown again. For example, if I key out my green screen, and then put a black and white effect on the footage, the green screen returns, but is now grey, and therefore I cannot add my background of choice. What if I want my effect to only affect whatever is not keyed out? I can't seem to make this work no matter what I do
You didn't mention how you applied the FX and which order you used. Actually when using the Chroma Keyer FX as Event FX, all you need to do is to apply the Black&White Event FX after the Chroma Keyer FX.