I think I've figured out what kind of Rose mallow I'm growing! Blue bird, a common blue variety that's been around for about a century, seems the most likely candidate.
But there's bad news in the clematis world today. My Roguchi got attacked by powdery mildew overnight. I gave it a hard pruning and took a few disease-free cuttings inside as insurance. I think it will bounce back quickly, but I probably won't get to enjoy many more blooms this year.
I should have doused then with neem oil or copper spray earlier in the spring/summer. Lesson learned!