Update 2: made the walls of the stem that inserts into the filament guide hole thicker, the old one broke. for some reason though the main section fills in solid but the lower half doesn't. maybe it has to do with maya (recently upgraded from maya 09 to maya 2014). currently i'm using the old top half and the new lower section and its working out nicely, but i still have to figure out just why the slicer decided to fill in the upper half of the colorizer.
Update: After fighting with the model since i uploaded this one, simply attempting to get the markers to fit properly and actually reach the filament i gave up and completely redesigned it from the ground up. this version only accepts one marker, i might remake it to accept two some other time. also the bottom doesn't fit snugly in the filament tube guide hole so it sits kind of loose. printing a rep 2 extruder upgrade right now in sharpie blue, so far the color seems nice and even. maybe more updates to come
Remix of CreativeTools Rep 1 & 2 dust filter
combined with cyclone's filament colorizer
colorizer part needed tweaking since sharpie markers didn't fit well with the original stl file. had to enlarge the holes the markers went into. WIP, may need more tweaking.