you can control from G-code or direct programming, but the http://goo.gl/dJpxac's doc is wrong, because the white color should be 50%, then mix up other color like the traditional 4 color printing. i have already done this type of program and tested with color sensor can change the color within 3mm filament, now i am working on the stepper position because 5 extruder is too big and will show later,