Let's say I have a dancer in a video wearing a red shirt. I'm trying to do an effect where the video is in black and white but I want just the shirt to be in color.

I tried to create two layers of the video. One in color and the other in BW and then try to apply a chroma key based on red to the BW layer.

It's not really working out and I'm not sure why.

For chroma key to work does it have to be an exact color of red or can it be shades of red ?

I'm not totally sure what to do with the compositing modes and compositing child parent setting.