Transparency in Preview

I've upgraded to 10.6. Nice improvement.

But one thing that is bugging me that I can't figure out. PDFs in Preview (v 5) keep showing the background as checkered background which makes lots of PDFs unreadable.

I assume this is because the background is transparent in the PDF. Is there a way to make Preview show this as white (I'm sure it used to do this)? The checkered pattern might be useful for editing, but not for reading PDFs.