I have recently noticed that on my 3 female characters, all which have become vampires, have lighter skin tones from the neck up than their bodies. Even if I reload a save before they had ever become vampires, I still get it. It is most noticeable on my Dark elf. Her skin neck down is dark brown, while neck up it is light green. I can not find anyway to fix this, and this was just recently noticed. I own Dawnguard and Dragonborn, and it seems to randomly fix itself and return at different times. Please help me if you know what this is.

I have noticed this too, and I think this is a problem with female (and male) characters no matter whether they are a vampire or not, although it might be more noticeable when they are a vampire. Like you said, the head and neck have a lighter skin tone (texture) than the reset of their bodies and I've also noticed that the neck seam is also sometimes very visible. I don't know if this bug was caused by the vampire appearance being tweaked with the Dawnguard DLC or not, because I didn't ever play a vampire until Dawnguard came out last summer. As far as a solution, I don't think there is one for those of us who play on the Xbox 360 console.