This is a very clever design by a man named Mat Beebe. He basically created a filament colorer using a single Sharpie marker. It runs the filament through the marker body and ink cartridge, before entering the extruder. It really works surprisingly well. There are 32 different colors of Sharpie markers, so this could be a big help for those that want to print in multiple colors but don't want to buy 30 rolls of filament. Read more and check out the video of this in action at http://3dprint.com/3340/ulimate-filament-colorer/