Very good Flycaster. That thought came to mind but I didn't want to ask the question - are you making home made wine? I'm pretty sure the answer would be no but it brought back great "I Love Lucy" memories.
I have purple ankles and feet as well. It's not exactly my favorite physical attribute. As it was explained to me by a couple of doctors, it's a failure of the vessel's hydraulic system. Valves aren't opening and closing quite right, so to speak, a variation on vericose veins, which I also have in my legs. I do lots of strenous walking for exercise and that makes the condition more apparent. I've had the condition for years. Where I work out, occasionally someone asks about it in the dressing room. It gives me the opportunity to say, with a straight face, "I work as a grape crusher in a winery".
I think it's time to see another doctor. Usually color change is tied to a circulatory problem. I know with Raynauds folks will have color changes from white to blue gray to red. My hands and feet turn dusky gray at times because of Raynauds. But a constant purplish color indicates a problem. Even if it turns out to be something not serious, it would be good to understand what's happening and why.