All key replacement technology relies on a 'clean chroma key' that software can remove to essentially mask the footage you want to keep and remove the parts of the shot you don't want to keep

The catch is, the replacement of the color is highly dependent on how 'clean' the key is ie: how uniformly lit your chromakey is. 

Virtual production allows filmmakers to utilize a combination of live action and cutting-edge digitally created environments rendered in real time on LED walls and ceilings (known as “volumes”) to deliver a production experience that traditional green screen sets couldn't match. Because the image projection in the volume matches the lighting on the actor the result of using volumes to film gives an incredibly flexible production environment that greatly reduces the post-production needed on a project.