[ghaff]

The article does mention diddling with the contrast and brightness as well as desaturating it. However, it doesn't give references to digital-based workflows working like this. I associate non-repro blue grids and pens with doing physical paste-up on a light table. I wouldn't think they'd be part of a typical digital flow although someone in that business would know better than I.

[Edit: As someone wrote, the article just seems confused. Yeah, you can adjust a digital B&W image so that a light blue goes away. You can also adjust it so a light yellow or a light anything goes away. Digital sensors do have different wavelength sensitivities but the use of non-repro blue and rubylith were a function of the specific sensitivities or lack thereof of litho film.]