If you have a new house and you are the sole owner, black is probably reliably neutral everywhere. If you have an older house, and just one previous owner was a careless do it yourselfer, then any color wire can carry any kind of charge.
You need a meter and a good dollop of paranoia tempered with (un)common sense to work on such a house.
Serously, get a polarity tester (little pluggy thing with a couple lights on it) and walk around your house with it. If you are not the first owner, I will give you ten to one that at least one outlet shows up flipped.