Preheat broiler. Combine 1 1/2 cups yogurt, 1/2 teaspoon salt, 1/8 teaspoon pepper, a pinch of saffron, and garlic in a large bowl. Add chicken, tossing to coat. Let stand at room temperature for 15 minutes. Place chicken on a broiler pan coated with cooking spray. Broil for 10 minutes per side, or until the chicken is cooked through and the surface is browned.