A typical chroma key set-up, using blue screen.
In visual effects, chroma keying is the process of removing a certain colour (often blue or green) from a live-action video. This was used in the Puppet Saga for the first time in Episode III, when Darth Daniel and Darth Elmo jump out of the ship into space, towards the planet Saturn. It was used the most in Episode IV, where all of the main characters, Kermit, Noah Tolmach, Darth Elmo and Darth Daniel fight while floating in Saturn orbit, above and on the surface of the moon Iapetus.