Remove skin from chicken. Rinse chicken, pat dry. Spray a 13 by 9 by 2 inch baking dish with nonstick coating. Arrange the chicken, meaty sides up, in dish. Brush with milk. In small bowl mix onion powder, thyme, garlic salt, white pepper, red pepper, and black pepper. Sprinkle over chicken. Bake in a 375 degree oven for 45 to 55 minutes or until the chicken is tender and no longer pink.