Hello and welcome to JustAnswer,
Wow, you are one of the few folks I know who can still find a dermatologist in a timely fashion. Did you ask your question of the dermatologist?
If it is truly a sun spot those can be lightened or removed with various creams or even a laser treatment in a similar fashion to the way tattoos are removed.
If you had your hair lightened then this spot may simply be more easily visible now than before with darker hair.
If you want definitive removal I would go back to the dermatologist and ask for it to be removed. If you want to try some skin lightening products I would also ask the dermatologist what he/she recommends as there are no shortage of them out there and since most are over the counter I have no idea which ones are likely to work well for you.
Please let me know if you have any more questions.