Why does or did Elsevier make PDFs grey and therefore unfit for printing? My university subscribes to various online journals. Sometimes I print off articles that I know I will read over and over again. (I'm all for saving paper, but some things I do prefer reading on paper. I print on recycled paper and I bind the articles, so they will last a lifetime.)

Now I tried to print an article from Advances in Mathematics (published by Elsevier) and it took me a while to figure out why part of the text was blurry: The PDF has seemingly random snippets that are not black (#000000), but in a dark grey (#231F20). On screen the difference is hardly noticeable



especially if it is text:



However, when trying to print it, the printer is trying to make it less than black, which results in blurry text:



As most other publishers manage to produce pure black PDFs, I must assume that this is intentional (it's not just "all italic text" or "all math mode symbols", the colour changes mid-sentence). The question is just why?

I doubt that this is an anti-piracy measure: surely there must be a less intrusive way of marking a PDF file digitally to record the IP from which a particular copy was downloaded. (Some journals add text like "downloaded from [this IP], [university name]", which I don't like, but at least the text itself is not blurry.)

I also doubt that it is to promote their offprint sales: Elsevier sells offprints of their articles, but only 25 copies or more and only to the original authors of the article (or someone acting on their behalf). In other words, it's not to "encourage" me to buy "quality" offprints of a single article of which I am not the author.

(Of course, it can't be to encourage purchasing of physical volumes/issues of the journal. It is entirely unreasonable to assume that researchers buy an actual volume/issue of the journal just for one article, if only because a single issue contains so many unrelated articles and researchers typically live in small offices.)

What benefit do publishers have from mutilating their PDF files?

Making a printable (= pure black) PDF would also have benefits: I'd be convinced that Elsevier is a great publishing company, publishing high-quality research papers in a good format for everyone's benefit and, as an author, would be more likely to consider publishing in Advances in Mathematics.

This also makes me wonder: 


Just to check, I am allowed to print PDF files (for use in research) of online journals, right?
Am I allowed to open the PDF in some other software, modifying the file so that it prints in pure black?
Am I allowed to use another method of getting a pure black printout of the PDF (e.g. by loading a special printer colour profile that treats the dark grey as black¹)?


¹ Unfortunately, I haven't found out if this is actually possible.

Note. I have not tried to investigate this issue systematically, but I observed this in 3 articles from Advances in Mathematics (Elsevier) from around 2005–2006.
This often happens when a document uses the CMYK color space and the black is set as (0,0,0,100).

When you go print in a monochrome environment, the document's color information is converted to grayscale first. Because black ink on white paper can't actually create gray, a halftoning process is applied, where the shades of gray are hinted at by using a circular-like pattern. 

Because CMYK (0,0,0,100) black isn't seen as being as black as it gets, in the conversion process, it gets turned into something more like 90% dark gray, and the halftone pattern appears.

Probably somewhere along the production process, someone got their blacks mixed up, and if it's consistent with all their PDFs it could be in the scripted part of the process, there's an issue either between color spaces (CMYK vs RGB) or a conflict between the source documents and the imported parts.