Nice coin. It reminds me of this one in my collection. I'm not sure about yours but mine is common, just not in this grade. German States Regensburg 1759 Heller
It's MS63. I purchased it from Karl Stephens at the WFOM the last time it was in Anaheim. I only got it because I had never seen one in mint state before. It was an inexpensive purchase.
It's a cool piece and neat you can see the curve from being struck on a roller die. They are very small coins!!
What makes you think the color is stable or 300 years old? It could have been toned a day before it was submitted to PCGS. It could be completely unstable and will change in a week.