That's the pen. It's available at practically every fabric store in America. I don't know if only one company makes them or not, but they're all purple. There used to be a light blue one, but I haven't seen that in years.

I've been using them for this purpose for close to 20 years, repeatedly on regular maps, with absolutely NO problem. I've never seen the ink color return. I don't see where they would be a problem on other paper, either, but I don't think I've used them on other types.

They are intended for fabric, and work well on that, too, although I think I've only used them on cotton and cotton blends.

Sue