Preheat oven to 425°F. Spray large rimmed baking sheet with nonstick spray. Arrange all bell peppers and tomatoes on prepared sheet, cut side up. Scatter onion and garlic over. Drizzle olive oil over vegetables; sprinkle with salt and pepper. Roast until peppers are soft and beginning to brown around edges, turning occasionally, about 1 hour. Remove from oven. Enclose yellow pepper in paper bag 10 minutes, then peel and finely chop. Reserve for garnish.
Transfer half of remaining roasted vegetable mixture, 1 cup broth, 1 tablespoon basil, and orange peel to blender and puree until smooth. Transfer to large saucepan. Puree remaining vegetable mixture and 3/4 cup broth in blender until smooth. Transfer to same saucepan. Thin soup with additional broth, if desired. Season to taste with salt and pepper. (Can be prepared 1 day ahead. Cover and refrigerate.)
Rewarm soup over medium heat, if desired. Ladle hot or chilled soup into 4 bowls. Sprinkle with reserved chopped yellow pepper and remaining 2 tablespoons basil and serve.
