Ah, yeah I see it now. That one in the upper right could possibly be a dragon tongue, but the green beans in the foreground 100% are not.
Immature pods on dt are skinnier, the purple is at its darkest, and they have a green tint. As they mature they lose the green and get more yellow between the purple, and when they’re fully mature the purple fades and they become almost completely yellow/white. I thought you might have grown a different bean because you described them as stringy and said they weren’t tender anymore by the time they developed their splotches, but my experience is that their splotches are darkest when they’re immature, and they stay tender without any stringiness until the seeds inside are developed enough for the pods to bulge. Could just be a difference in climate for all I know (I’m in the high desert).
Attached picture is a pile of dt bean pods I harvested in various stages of ripeness.
One of my all-time favorites!