Kneel before Zo... I mean, hey look what you can do with experimental dual extruders on a MakerBot - grayscale vector art. This is an attempt to show how by designing your model so that you vary the number of layers between two colors, you can do some simple color mixing.
For more info on how to make shapes in inkscape and extrude them in openscad, see: http://tonybuser.com/2d-to-3d
You will need to use at least Skeinforge 40 to slice these models. Skeinforge 35 has a bug where shapes enclosed inside other shapes cause the shapes inside to have 0 infill.
The models have an extra layer on top because of a bug in replicatorg where it doesn't print the top layer in a dual extrusion operation... luckily it will be easy to change by modifying the scad script.