[LearnAutoBody]

Well, clear coat sands to a white color, but that would not be the case since you didn't clear the car. Then I thought maybe you sanded through your black paint, but your sealer is dark gray. Could it be the color of the primer you used? What color was the car to begin with? Do you know where the dirt may have came from? If this is in on one panel I would repaint the panel and buff the rest of the car. However, if it is the entire car, it may be best to shoot the car again. Remember that black is the hardest color to buff because it shows swirl marks more.

If you re-paint the car, make sure the car is clean. You may consider the dust is coming from you. Make sure that you are clean. Use a paint suite. If you are only going to paint one or two panels, make sure that you cover the rest of the car with plastic to protect it from overspray.

Do you have any pics?