Got my PW yesterday and it has some of that same mottling. I like it. It reminds me of parchment rather than velum. Since this is the Internet, let me get there first: Kindle Parchmentwhite. I still like it.
Who was it that said the perfect is the enemy of the good. Since perfect doesn't exit I prefer to see the KPW for what it does have: a highly readable screen in any light and a really great source of content.