A relatively early color video clip, from November 1, 1959, finds Milton Berle parodying the old routines he used to do. And he uses chroma-key technology to present two “Miltons” on camera simultaneously.

Filmmaker IQ provides a quick history of chroma-key:

http://filmmakeriq.com/lessons/hollywoods-history-of-faking-it-the-evolution-of-greenscreen-compositing/