Russian Herring Salad Covered in Beets (Fur Coat)

Name: Russian Herring Salad Covered in Beets (Fur Coat)
Cuisine: European, Eastern European
Ingredients: 3 large beets; 3 large potatoes; 4 large carrots; 1 1/2 cups mayonnaise, divided; 1 medium red onion, finely chopped, divided; 4 fillets of pickled herring in oil, finely chopped; 4 large hard-boiled eggs, finely chopped; Black pepper, to taste; 2 large hard-boiled eggs, sliced, optional; Fresh dill or parsley, chopped, for garnish