Marker holder (for colouring feedstock)

We bought lots of white ABS with our shapercube.. Lots. But who wants
to print everything in white? After a while that got a
bit.. samey. So, an experiment, jam a coloured marker in the feedstock
inlet and see what happens. What happened was, coloured prints came
out. So the idea for the marker organ was born, a way to attached
several coloured markers to the feedstock, and pick which one, or
combination, is colouring the plastic.

This is the first attempt, a simple clamp over the feedstock which
holds a single marker against it.