Kicked Up Cole Slaw

3/4 cup mayonnaise
1/4 cup Dijon mustard
1/4 cup packed light brown sugar
3 tablespoons apple cider vinegar
2 tablespoons buttermilk
4 teaspoons celery seeds
1 teaspoon salt
1/4 teaspoon freshly ground black pepper
1/8 teaspoon cayenne
3 cups shredded green cabbage (about 1/2 head cabbage)
3 cups shredded red cabbage (about 1/2 head cabbage)
1 green bell pepper, finely diced
1 large carrot, peeled and shredded
1/2 cup grated yellow onion
1/4 cup minced fresh parsley

In a bowl, combine the mayonnaise, mustard, sugar, vinegar, buttermilk, celery seeds, salt, pepper, and cayenne, and whisk well to dissolve the sugar.
In a large bowl, combine the remaining ingredients. Toss with the dressing until evenly coated. Adjust seasoning, to taste. Place in the refrigerator, covered, to chill slightly before serving.