Bring a large pot of salted water to a boil. Add macaroni and cook until al dente, about 9 minutes. Rinse under cold water to stop cooking then drain well.
In a medium bowl make a dressing by whisking together mayo, condensed milk, vinegar, paprika, mustard, salt and black pepper until smooth
In a large bowl add the cooked pasta, onion, green and red bell peppers, celery and whisked dressing. Fold gently until well combined. Refrigerate overnight and serve.