The UltiPanel makers did the Filament change command to make their LCD display more desirable. When the Marlin firmware gets an M600 command, it pulls the nozzle away from the print and turns off the extruder motor so you can manually replace what ever filament is currently in the machine. It takes time to purge the existing color out of the nozzle. Going from light to dark doesn't take very long. But going from black back to white is a slow process. Rather than manually do it... On the Iris box, it looks kind of nice to let the black band fade back to white.

This command is useful when doing novelty items like 3D Printed business cards! I've made some of those and they definitely get some attention during the interview process.

If you have a free switch and GPIO on your electronics, you can give the command a try. It works pretty well, but you need to be by your printer when the change over happens.