Purple green beans

This morning I found these purple green beans (hello, oxymoron!) at the farmer's market in Fort Greene. I have never seen purple green beans before, and the interesting thing is that they are only purple on the outside. When you snap them open, they are green on the inside. Which goes to show that green beans will always be green beans no matter what color they are — even if they are purple. And apparently the purple beans turn back to green when you cook them, which is even more intriguing.