If you cant find the baby potatoes specified here, substitute 1 1/2 pounds of any varietythe salad will still be delicious.
Make vinaigrette: In large bowl or blender, mix or blend all ingredients until well combined. Set aside.
Bring large saucepan of water to a boil. Add beans and cook until bright green, 2 1/2 to 3 minutes. Drain, rinse under cold running water and drain well. Transfer to small bowl. Add 2 teaspoons vinaigrette, toss to coat and set aside.
Peel purple potatoes, cut into quarters or 1-inch pieces and place in medium saucepan. Add water to cover by 2 inches and a pinch of salt and bring to a boil over medium heat. Cook until tender, 8 to 10 minutes. Using slotted spoon, transfer potatoes to medium bowl. Add 1 1/2 tablespoons vinaigrette to warm potatoes and toss gently. Set aside.
Prepare and cook white potatoes as above; transfer to separate bowl and toss with another 1 1/2 tablespoons vinaigrette. Keep potatoes separate until they have cooled to room temperature.
Meanwhile, slice beans into thin diagonal strips about 1 inch long; cut tomatoes in half. Set aside. In large bowl, combine cooled potatoes, celery, red onion, parsley and pickle. Using spatula, gently toss with remaining vinaigrette, as needed. Season with salt and freshly ground pepper to taste. Garnish with green beans and tomato halves and serve.