When it's being made, paper is not white, so in the process it has to be bleached.(Though not all of it, for some reason.) It was then thought to be 'greener' if recycled paper was added to the mix, but still bleached, even more so. That bleach-filled water ended up in rivers. The manufactures were forced by law to some how stop that, and they did, costing vast sums of money.
Then some lateral thinking bright spark, thought, hang on, why does it all have to be white? So they stopped bleaching all but some instances of usage, and few people bothered about it not all being white. In fact they approve that it's not bleached and possibly partly recycled.
Books. If you look at the pages of most books' white paper they are not pure white. Not even coloured (unless they are of course, such as cream, which is pure white paper, dyed ...) They are a sort of faint 'natural' biscuit shade. (With most paperbacks that's almost always been the trend.) It's not bleached to death, if bleached at all.
The bottom line of this shaggy dog story is, the paper Lulu's printers use is pure virgin white and glares out like a lamp from amongst other books on a book shelf. Bleached to within an inch of its life it has to be assumed. But does it need to be when the paper in most other books is not?
Text is in fact easier to read on off-white.