Was this your first free service at 6 months/5k miles? If so they don't change the oil on that service. They rotate the tires and check the brakes and fluids only. At 12 months/10k miles they do all of that again and also change the oil and filter.First time this happened to me. I just went to a toyota dealer for my free oil change. After the oil change I checked the oil and its dirty. Never changed it. The color is dark.