Pale skin is either a sign of albinism or that you're some sort of unnatural fiend sent from the depths of hell to wreak havoc on those who have pigment in their skin. And due to Alucard's blood-sucking fangs, one would likely guess that he's the latter.
Who he really is:
Unfortunately for Castlevania's Alucard, he is not a fiend sent to eradicate humans, meaning he is most likely the world's first and only albino vampire with a heart of gold. Hopefully he's also the last.