Brining Pork Turns Meat Grey
Yes, that's normal.  You just left it WAY too long in the brine.  The salt denatures (unwinds) the proteins, which is the same process that happens when the proteins are exposed to heat or acid.  Over brining will cause the exterior of the meat to become gray and mushy.

But you don't have to take my word for it: http://www.cooksillustrated.com/how_tos/5804-brining-meat

The relevant references are:


4 bone-in rib loin pork chops, 12 ounces each, 1.5 inches thick: 1
hour
Pork roast, 3-6 pounds: 1.5 - 2 hours