2 pounds red potatoes, cut into 1-inch chunks
1 pound sweet potatoes, peeled and cut in 1-inch chunks
1/4 cup red wine vinegar
1 tablespoon spicy brown mustard
1 1/4 teaspoons salt
1/2 teaspoon pepper
1/2 cup reduced-fat mayonnaise
1/4 cup 2% milk
2 celery ribs, chopped
1 small red onion, chopped
1/3 cup minced fresh parsley