I've always been pale, even though my father has quite dark skin. now (in my late teens),i find my skin darkening. could this be caused by genetics?

Yes. Get a check-up.: That's what regular check-ups are for... to make sure that gradual changes in one's body over time are indeed normal gradual changes. Nobody has the same skin she had as a baby, unless she is still a toddler or preschooler. Most changes in skin color are normal but one's primary care doctor can check to be sure. Rarely are people darkened by hormonal disorders. Otherwise, any normal color is fine.