Why did Kaneki's hair turn back to its original colour? At the end of season 2, Kaneki's hair turns back to its original colour.

I know his hair turned to white because of the Marie Antoinette (MA) syndrome, but in all the research I've done, I've found nothing regarding a cure for the MA syndrome.

So, why did his hair change back? Can the MA syndrome be cured? And why did Kaneki get cured out of the blue for no reason at all?
My interpretation was that it was purely symbolic. I saw the white hair as a change in his personality, a sort of draining of his "color" or original personality. When his hair changes back, we see some of his old self coming back.
Keep in mind that writers don't necessarily make those sorts of decisions with medical backing. Pure symbolism is often a very large factor.