This is a calibration cube with a pattern for printing on a 2 extruder printer and fine tune the extruder offsets and other printing parameters.

There are 2 STLs. The ColorBase.stl is to be printed with one extruder the ColorPattern.stl with another. The Sketchup file has both pieces together each piece as a component.

Use Skeinforge to slice. The STLs are sliced separately. Make sure both objects end up in exactly the same spot and the skirt (if used) doesn't overlap with the object. Both objects have to be slices with the same layer height. The penultimate gcode has to be generated. Pass the penultimte gcode file names for the base and the pattern to the addcolor.pl script as the first two parameters, and the names of the files with gcode for switching to the secondary extruder and back as the 3rd and 4th parameters. The merged gcode is printed to stdout (the comments are stripped and it should be ready for printing).

There are more details on the mod for the printer here:
http://www.thingiverse.com/thing:16523

The pictures show the results of printing at 50mm/sec, 0.5mm nozzles.
PLA: orange/transparent(natural) and red/blue pieces
ABS: black/white(natural)

The video for printing one of the ABS pieces is here:
http://youtu.be/GVVmdrmvYq8