It is tough to say without pics or seeing it in person, but what you are describing sounds similar to something I've noticed with one of my amels.
Both on his head and on numerous spots down the sides of his belly he has spots that look almost translucent (grayish in color). In his case, it's completely normal and nothing to worry about. I can't say for sure if it's the same thing you're seeing. I've looked through a lot of the pics on my computer and can't find a good example of it. I'll poke around a bit more and see if I can't turn something up.
Jackpot!
Okay, I found some pics. The one of the head is obvious. The one on his side is much more difficult to see in pictures. In person, it has a more grayish color to it. It's not white like the rest of the areas you see on him. It's more like it has no color at all. Hope this is of some help to you.