Usually single tooth whitening is a concern for teeth that have had root canals, or need root canals. If they have had a root canal you can bleach it from the inside. If they haven't, you may do a root canal and that may be enough. Often the tooth that has had a root canal needs a crown and can be matched with a cosmetically designed crown.
Trying to whiten one teeth is a toughy and most of the time the success rate is very low to minimal. A single veneer can be done if the color is really off. A good cosmetic dentist is your best source of information...Dr Thomas