Purple Potato Salad

Bring a pot of salted water to a boil. Boil the potatoes until fork tender but not mushy, about 20 minutes. Drain, then rinse in cold water, and cut in quarters. Place the warm potatoes in a large bowl and toss with onion, celery, dill, and parsley. In another bowl, stir together mayonnaise , mustard, celery seed , cayenne, vinegar, and lemon. Check seasoning. Add the dressing to the vegetable mixture. Toss gently to coat taking care not to mash the potatoes. Season with salt and pepper.