I think this subject was discussed some years ago on the board and the consensus was that the borders can "tarnish" and wear over time, exposing any color underneath them. We know for sure from misprints that the gold was the last ink applied and that the black was next to last:
Stands to reason that if the gold is worn off, the underlying colors would be exposed. I don't recall seeing one that was in nice shape but green bordered. Below is one from a small find of T cards some years ago. I could not believe how bright the borders of the T205s were, but on this one the lower right border has started to tarnish and wear and looks to me like the underlying color is starting to show through.
