Why does or did Elsevier make PDFs grey and therefore unfit for printing?
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.