Step 1Combine cabbage, onion and peppers in plastic, glass or stainless-steel bowl. Sprinkle with sugar. Set aside.
Step 2Combine vinegar, oil, salt, mustard and celery seeds in saucepan and bring to boil, stirring occasionally. Remove from heat and immediately pour dressing over cabbage mixture. Do not mix. Cover and refrigerate 24 hours. Mix well before serving.