Bring a large pot of salted water to a rolling boil. Add rotini pasta and cook according to package instructions, usually about 8–10 minutes, until al dente. Drain and rinse under cold water to cool.

Pour 1/3 cup of dill pickle juice over the cooled pasta. Toss gently to coat and let marinate for about 10 minutes.

Chop the baby dill pickles, dice the Colby Jack cheese, and finely chop the white onion.

Drain the pasta, transfer to a mixing bowl, and fold in chopped pickles, cheese, and onion.

In a separate bowl, whisk together mayonnaise, sour cream, dill pickle juice, fresh dill, salt, and pepper.

Pour the dressing over the pasta mixture, tossing to coat evenly. Chill for at least 1–2 hours.

Serve chilled, garnished with additional fresh dill if desired.