Filament Dye - Cheap and Simple

So, I was printing some bar clamps for the Prusa Mendel and an odd idea popped into my head and before I knew it, I was rubbing dry erase marker on the filament prior to printing. About half way through the build I noticed that the filament being laid down was changing color. It appears as though the filament is being extruded without any halt, error, or otherwise. The dyed filament adheres to the HBP of my Thing-o-matic just as regular filament would. The layering is identical, and no other err