Prepare the buttermilk ranch dressing and refrigerate overnight.

Boil the tri-colored corkscrew macaroni according to package directions.

Boil the plain corkscrew macaroni according to package directions.

Rinse both types of pasta with cold water and drain thoroughly.

In a large bowl, combine the cooked pasta, chopped chicken, diced celery, red grapes, green grapes, and mandarin orange segments.

Pour the prepared buttermilk ranch dressing over the salad.

Toss well to ensure all ingredients are evenly coated with dressing.

Cover the bowl tightly with plastic wrap or a lid.

Chill the salad in the refrigerator for at least 1 hour before serving.