Hey,
There is absolutely NOTHING permanent at the moment apart from depigmenting your skin using a depigmentor (such as monobenzone) but even this in rare cases can result in full repigmentation and sometimes even hyperpigmentation after you stop the treatment. If that happens it could be more difficult (even impossible) to remove the pigment again.
Hydroquinone does work in lightening your skin but it is not permanent and to maintain your colour you need to keep applying it and stay out of the sun. A lot of scientists suggest that long-term use can result to skin cancer.
There might (quite possibly), in the future (how soon I do not know), be a method of lightening or even depigmenting your skin by knocking or altering some of your genes (i.e. genes that produce melanin). It is still not available because 1. knocking the melanin gene out can result in losing your hair melanin etc as some genes code for more proteins than one and 2. Obviously because of the ethical issues.
A