For dressing, in a small bowl, combine the mustard, vinegar, sour cream, ketchup, mayonnaise, salt and cayenne. Stir in the sugar.
In a large bowl, combine the cabbage, onion, green pepper, carrot and celery. Add desired amount of dressing; toss until well coated. Refrigerate until serving. Refrigerate any leftover dressing. Serve with a slotted spoon.