I don't really agree that the advice not to use black-on-white implies using light-grey-on-white. It's possible for designers to interpret that advice poorly, a

I don't really agree that the advice not to use black-on-white implies using light-grey-on-white. It's possible for designers to interpret that advice poorly, as the author shows. Think of Knuth's warning against "premature optimization" and all the dumb decisions that have been justified on the basis of a poor interpretation of Knuth.