I am assuming that the purple spots are visible no matter what app or screen you are on? Just to see what's going on, I'd completely power down the device and restart it. If the spots are in the same location or continue to grow, then its probably something physical....like the LCD going bad. Any trauma to the device? Did it experience an unusual amount of pressure or force on the screen? If not, then maybe its just an internal issue that should be covered under warranty.
Unfortunately being 2 weeks away from your home address might not help. Normally, ATT sends out a device the same day for warranty exchanges. I don't know if they ship to a location not on record. You'd have to call them and ask if anything can be done...but first you need to be sure its eligible for an exchange or you'll end up buying another Active.
Good luck