Cut tomatoes in half. Thread onto skewers, alternating colors. Brush with 1 tablespoon oil; sprinkle with salt and pepper.
Grill, covered with grill lid, over medium heat (300° to 350°) for 10 minutes, turning skewers often. Combine remaining 2 tablespoons oil, vinegar, and chopped basil; drizzle over kabobs. Garnish with fresh basil sprigs if desired.
Yield: Six servings.