Even on my white Z06 with the OEM metallic pads (TONS of dust) I had no issues with washing the car and removing the dust. That's odd. When's t he last time you waxed it?It is brake dust. Had the same thing on our white Pontiac Vibe. The issue is it does not come off the paint easily.
I am just not totally sure if it is the pads or the thin layer of rust on the rotors (that forms when the car sits overnight) flaking off upon braking when using the car the next day.
On the Vibe this did improve a lot when I put on new pads (which were ProACT).