It's a very light scratching, more than a rub, but be careful you don't scratch too hard or you may leave scratches in the plastic underneath. If in doubt, don't do it, and I aint responsible if you do anyhting that damages it.
Disclaimer out of the way, here are pics. Sorry about the quality, but my room really hates photographs in it and always makes them dark, despite there being more than enough light in real life. Believe it or not, the main light was on.
This is the arm completely removed. As you can (or perhaps not) see, the black has been removed and the red is left intact underneath.

This is an arm that I really should go back to and finish. This is so you can see what it eventually looks like as it's being removed. But this will take many months to do, so be warned.