Murphy's skin
I have a theory on why Murphy's skin is losing it's blue hue. Maybe it's because when he bites people to control them, he's sort of spreading himself thin amongst all those people. As his "zombie-ness" goes into other people, he loses another little piece of it.
The other possibility I was thinking of is maybe it has something to do with him eating brains. Maybe as he eats the brains he ingests a little more humanity into him. Does anyone remember if his skin started turning white before or after he started eating the brains?
Apologies if they've already explained this. Sometimes I don't pay as close attention to this show as I might.