It's certainly true that there are materials that are good absorbers of IR. I had a quick look and note that they are usually either dark brown or dark green dyes. However, these are specialist materials (could this account for why the pens are so dear?).

Nevertheless, it remains my understanding that black absorbs all wavelengths - this, after all, is the definition of black, the complete absorption of all colours and the reflection of none, so green remains a mystery.

In any case, I'll cancel my experiment, as I cannot assure a green colour that would match that of the stoplight pen and I'm too mean to buy the real thing!