If you notice any type of discoloration in the flesh, you should not buy them (this is especially true if you see any black spots). This may mean that they were not handled properly. This can mean they won’t taste as good as they should or, worse, they can make you sick.
If the lobster tail has a grayish color, you should not buy them. This is a sign that the lobster was not alive during processing, which means it will not taste as good.
If the meat looks yellowish, you should not buy it. This may mean that the lobster is not as fresh.