Spill suppression

Chroma key removes the background. Spill is what the background left behind: a green rim along the shoulders and a tint running through loose hair. Suppression tools desaturate or replace that colour at the edges so the subject sits properly against whatever is behind them now.

Software only gets you so far. Most spill comes from standing too close to the screen, so a metre or two of separation plus a light on the subject that the screen is not providing removes it at source and leaves the plugin far less to do. Over-aggressive suppression has its own look. It turns skin grey and eats the fine strands of hair at the edges.