I was at Home Depot last night, so I figured I would get a couple of spare keys made for my WJ. I was told by the guy at Home Depot who is an owner of a Chrysler vehicle, that the gray keys have chips in them for the security system. If you get a copy made at a place like Home Depot, the keys will unlock the vehicle but won't start it. This could be used to hide on your vehicle in case you lock your keys in your vehicle. The black keys don't have chips in them.
There was another thread from a guy in SF that lost his keys. I was wondering why people were stating such different prices for getting keys made. This is why.