It’s about 3D printing with multiple (rainbow) colors using 1 extruder.
The Prusa color site mentioned in the video to help you print multiple colors and have fun doing so.
Notice that using this, you can change the color from a layer heigth to another layer height. This is not a true print in multiple colors.
This is not a DIY tutorial. Watch for fun, please comment and let us know your thoughts, tell us how you would have done this.
And always remember… safety first, so always watch out for electrical and mechanical dangers, wear proper safety equipment and don’t play with devices or substances that you do not understand. At the end of the day, you want to keep all your fingers intact for the next day.