Black flakes from new cast iron pan
It sounds to me like the washing process (and subsequent attempt to re-season) broke down the pre-seasoning and you are losing the oil coating on the pan. When you see the "ashy grey" color, what you are seeing is unseasoned cast iron.

The good news is that it's certainly not unsafe to cook with, even in this state. The black coating is just oil that has been baked onto the surface of the pan, giving it a low/nonstick surface. Totally safe for consumption.

To get your pan back to its best state, you'll need to re-season it. There are a number of good tutorials on the process (such as http://www.thekitchn.com/how-to-season-a-cast-iron-skillet-cleaning-lessons-from-the-kitchn-107614), but it is really quite simple:

1.) Clean your pan well

2.) Apply a coating of fat to your pan - I prefer lard, flaxseed oil, crisco, or vegetable oil (in that order)

3.) Place your pan upside down on the top rack in a 350 degree oven, and bake it for at least 1 hr. I suggest putting a roasting pan or foil on the bottom rack to catch any oil that drips out of the pan during the process

4.) Let cool in the oven, and wipe down gently when done. Your pan is seasoned and ready to use!

After you've seasoned your pan, it's important to make sure you are using the proper cleaning approach to preserve your pan's surface. The ideal way to clean your cast iron is immediately after cooking in it, while it is still hot. Use warm water and a sponge, and then immediately dry it. If you need an abrasive to get stuck-on food off, use some salt and scrub gently.

Never use soap, or highly abrasive cleaning pads (brillo, metal scrubbers, etc). These will strip that non-stick, baked on oil surface and make your pan much less enjoyable to cook with. The good news is that if you ever slip up and notice that the surface has been stripped, you just need to repeat the seasoning process and you should be good to go again. 

Hope that helps!