If you are choosing a live lobster from a tank at a restaurant or from a live seafood dealer, the most important thing to look for is the lobster’s activity and the shape of the lobster’s tail.
Look for a lobster that seems active and alive, and the more active, the better. The lobster should be moving around and holding its claws upwards; avoid lobsters whose claws hang limp. And look for a lobster whose tail is straight; never pick a lobster whose tail is curled while it is still alive.
Color is not an important factor in picking a lobster, since healthy lobsters come in a range of colors from green to brown to black, and other colors. (All lobsters — except rare white lobsters — turn bright red when cooked.