In a large mixing bowl, combine the shredded green cabbage, shredded purple cabbage, grated carrots, sliced red and yellow bell peppers, thinly sliced red onion, chopped parsley, and chopped cilantro (if using).
In a separate small bowl, whisk together the Greek yogurt, apple cider vinegar, honey or maple syrup, Dijon mustard, salt, and pepper. Adjust the sweetness and seasoning to taste.
Pour the dressing over the vegetable mixture in the large bowl.
Toss the vegetables and dressing together until well-coated. Make sure the dressing is evenly distributed throughout the slaw.
If using, sprinkle the chopped toasted almonds or sunflower seeds over the top of the slaw for an extra layer of texture.
Allow the Rainbow Cole Slaw to chill in the refrigerator for at least 30 minutes before serving. This allows the flavors to meld and the slaw to become even more delicious.
Serve the Rainbow Cole Slaw as a colorful and refreshing side dish alongside grilled meats, sandwiches, or other main dishes.