Combine the green and purple cabbage into a bowl or salad spinner and sprinkler the salt and sugar over the top. Slightly toss until coated and let sit for about 5-10 minutes. This will brine the cabbage and help keep it crispy after adding the dressing.
Rinse the cabbage and spin dry in a salad spinner or pat dry with paper towels. Then, add the carrots and onions and set aside while you mix the dressing.
For the dressing, combine all the ingredients and mix until smooth. Then add to the salad mixture and toss until covered. It’s ready to serve or can be chilled in the fridge until needed!