My 2006 isn't the best to compare to, it's been in a case for most of it's life. But I've seen other white Gibson's from around the same time, that have been gigged heavily, that aren't that colour. Always more of a creamy yellowish, but not brown like that. I think @Gaolee is right, the owner smoked heavily in his studio.
If it is from smoking, that's just nasty.

