Look in the Swatches panels of InDesign and Illustrator, and the Colors list in QuarkXPress, and you’ll see a mystery color named “Registration.” It’s intended for page information, registration marks, and trim marks. When we used to output film and strip it up on light tables, we used registration marks to ensure that all the inks printed in alignment. Registration is intended for use only by the application, not the user, except in rare cases.
Because of the wide usage of direct-to-plate workflows, few printing companies are still outputting and manually stripping film, although I suppose it may be going on in the hinterlands. The only exception would be specialized printing processes, such as screen printing or metal etching. While registration marks and other locating marks are used on press to monitor ink alignment, those marks are usually generated by the imposition software that positions the pages for output, rather than the original page layout or illustration applications.
What color, exactly, is Registration? It’s all the inks used in the document: it’s 100% of all inks. So, in a job containing CMYK plus PMS 185, Registration would be C100-M100-Y100-K100 plus 100% PMS 185. This adds up to a whopping 500% ink coverage where Registration is used. This is not a press problem in isolated areas such as trim and registration marks, but such heavy ink coverage in larger areas would result in drying issues and other problems. And if there’s slight misregistration on press, you’ll get a bleary multicolored fringe:
Why do I bring this up? Because twice this week I encountered files built with Registration instead of plain old Black. If there had been just one element — say, a line of text — using Registration, I would have chalked it up to mis-clicking: aiming for Black, and accidentally hitting the next color in the list. But, no: in both cases, Registration had been used for all the text in the InDesign page, as well as artwork created in Illustrator. Clearly, it was intentional. But why?
My guess is that the designer thought plain old Black just wasn’t robust enough; maybe it looked anemic on their desktop printer. And it’s true that process black ink alone in large areas can look, well, gray rather than black: that’s why we use rich black builds in large areas. Registration is not an appropriate “rich black,” however!
If your design contains large bold black text (40 pt or above), or large solid black areas, consider using a rich black build (try C40-K100). Better yet, ask your printer what they’d recommend for a rich black recipe, as well as their advice on where to use it (i.e., text size or color area dimension).
I wish the applications wouldn’t even display Registration; maybe it should be a hidden color choice, available only from a subsidiary panel menu in the Swatches and Color panels. Until then, you’ll have to police yourself: don’t click there!