it sounds like you may have a little bit of a green light reflecting off of the subjects siloette(?)/outline. try adjusting the hue a little bit before keying….that’s how i’ve always done it in avid. or, I could just be way off.
I’m trying to change a solid’s color instantaneously. I’d have to set keyframes 1-2 frames apart to achieve that hue/saturation, causing a ‘flash’ as it tries to go through the color spectrum