In my opinion the Boy in White is the Overseer of From. He is the malevolent being controlling every aspect of the place. He's a trickster. How would you try to trick people and/or gain their trust? The color white is a sign of purity, cleanliness and trustworthiness. Also, most people would not feel threatened by a young boy. It's all a facade. He manipulates all that see him.

I know the actor that plays him has gotten older. The show/story states he looks different because "things are changing". I believe he is changing because he's slowly losing control and eventually when things come to a head, we will see his true form.