Stir together the drained and cooled pasta, both cabbage, the shredded carrot, diced celery and bell pepper and chopped scallions in a large mixing bowl.

In a small mixing bowl, whisk together the mayo, vinegar, sour cream, sugar and celery seed. Taste and adjust seasoning, if you like, with salt and pepper.

Pour the dressing over the pasta and vegetables and fold together until well combined. Salad is ready to serve but actually improves if let to sit for at least 1 hour for flavors to meld. Salad can be refrigerated overnight in an airtight container. Bring to room temperature before serving - or at the most serve it just lightly chilled. Salad can keep, refrigerated, for up to 3 days.