Add the dressing to the potatoes and toss to coat. Finely chop 3 hard-boiled eggs and add to the potatoes along with celery, pimientos, olives, parsley, chives (or scallion greens), the remaining 1/4 teaspoon salt and pepper. Stir gently to mix. Transfer to a serving dish and sprinkle with paprika. Slice the remaining egg and arrange the slices decoratively on top. Garnish with chives (or parsley sprigs).