Here's a picture of the 'milkiness':
It's only noticeable in direct light.
As I said before, since it's smooth and not sticky I assume that it's damage, though I really have no experience with this. I also don't know if the area is clear or paint, and if it is paint, if it is acrylic, enamel, etc. (metallic paint is usually enamel?). Thus I'm not sure what kind of cleaner would be safe to use (citrus, acetone, wd-40, polishing cream, etc.)
As for getting a replacement decal, I would have to say I'd rather be stuck with the milkiness; I'm not a fan of bright red on metallic green.