RGB injected at different rates with a mixing head. Simple Yes each separate colour is laid down at once per layer then the next colour until layer finished. Simplify each process until it can be understood in a mechanical action. What about using custom G-code or M-codes? http://linuxcnc.org/docs/html/gcode/gcode.html http://linuxcnc.org/docs/html/gcode/m-code.html