I can speak for people of the Indian subcontinent - we have a variety of skin colours that are prone to tan. Our skin colour also kinda changes throughout. I notice a change in my skin colour as I grow older, but not drastically. Problem with tan is that it's not that easy to get rid of it, especially if you keep up activities such as swimming in daylight in an outdoors pool.
I doubt if your skin colour has CHANGED permanently, but if you were to give up say, swimming for a few months and see if it gets back to normal. Or use bleach?
I acquired a tan in January from the beach which is still pretty much there 6 months later.