White = bleached = unhealthy. Brown is the natural color, because when zooantha grows within their body / tenticles they start to turn a dark brown / greenish color / tint. The only BTA colors that I know of are brown (most have this tint anyways) rose, and green (again most have this tint).
A white anemone (BTA, LTA, Sabae) are unhealthy and do not have the light feeding algae in their body that they need to survive long-term. If the entire anemone is white (including the foot) i wouldn't purchase it, if just the tenticles are white and the foot / base is brownish, then under the proper lighting it can recover.
Sorry for the crap pictures...