The "double i3" is a prusa i3 clone on which a second vertical frame is mounted. The first frame is for extrudeing plastic like a normal i3. The other frame is used for adding colour. The second frame works with a colorpod.
First experiments are done with clear PLA and water based ink. After a plastic layer is laid down the build plate moves to under the second frame where colour is added in the form of cyan, yellow and magenta ink.
This setup is build from 2 Geeetech Prusa I3 pro C kits. It prints the model with layers of 0.2mm.