The Hebrew blue book

Once upon a time, I used to deal in old Hebrew books.  I still have  few of them; I kept the ones that I found most interesting.  Some of those books were printed on blue paper and they hail from early 19th century Ukraine.
In an article about an online gallery of rare Hebrew books, we are told why blue paper was used:

“My favorite pieces in the exhibit are the books printed on blue paper,” says Mr. Hill. “The blue paper was cheaper than better-made white paper and therefore more accessible to indigent wandering printers,” he explains. “So many Hebrew books were printed on this blue or ‘bluish’ paper that it became associated in popular imagination with old Hebrew books. The memory of this paper, which was used in the decades before and after 1800, remained vivid in the minds of writers born in Eastern Europe well into the 20th century.”

When I used to deal in such old books, I remember being told that the reason books were printed in blue is that the Russian government imposed a high tax on regular paper and the tax did not apply to the cheaper blue paper.  Here are a couple of blue books from my collection (Sadilkov 1835):

This one was printed in the village where my grandfather was born and it has only a slightly blue hue (Mezibuzh 1819):