Combine the all of the cabbage in a large colander along with the salt, toss, and set in the sink to drain for 3 hours.
Thoroughly rinse the cabbage under cool running water for at least 1 minute. Transfer the cabbage to a salad spinner to dry thoroughly.
Whisk together the buttermilk, yogurt, mayonnaise, pickle juice, mustard powder, and black pepper in a large mixing bowl. Add the cabbage, carrot, and chives, and toss to combine. Serve immediately, or store in the refrigerator for up to 3 days.