1. Shred cabbage, onion, and green pepper in a large bowl.
2. Pour sugar over mixture; do not stir.
3. Combine vinegar, oil, celery seed, salt, pepper, and dry mustard. Bring to a rolling boil.
4. Pour over cabbage mixture while hot; do not stir.
5. Refrigerate for at least 12 hours.
6. Stir well before serving.