"The folks from Krakow-based Pirx have been making basic personal 3D printers for a while now, but lately they’ve been working on a new machine that could be able to print in full RGB color. At the moment they have only a prototype, which they recently displayed at the London 3D Printshow.
Do they use multiple extruders? No. Do they mix differently colored filament in a single nozzle to create arbitrary colors? No. Then how do they do it?
They’ve been inspired by those who have experimented with marker pens adding color to the filament just as it enters the extruder. That method is quite crude, but does demonstrate that it is possible to “ink” filament during extrusion.
The Pirx color solution involves the installation of a 2D color inkjet printhead on the extruder. The inkjet can theoretically squirt out any RGB color on demand and change colors very rapidly. By carefully coordinating the mechanics, the Pirx team believes they can actually color printed objects. In the image above, you can see how they placed spot color on a section of a cup.”