There are a number of possibilities for why this is happening.
First, are these objects REALLY grayscale? Make sure the color mode is grayscale and not RGB or CMYK on images and they just look gray.
Second, is the PDF destination profile the same as the CMYK working space in the document? If there is a conversion during export, your K-only blacks and grays will get converted to 4-color mixes.
Third, if you include any printer's marks in the export, those will be Registration color and generate a color click.
If printing to the copier, can you control CMYK vs. K only output from the driver?
For PDF workflows, you should have control at the DFE/RIP driving the copier to specify/override which pages are rendered in CMYK and which in K only.
Otherwise I would recommend a PDF editing tool such as Enfocus PitStop Pro for absolute control, as Acrobat Pro preflights/fixups only go so far (in Acrobat Pro X the convert Registration/All “colour” is broken, while in Acrobat 9 it worked). Colour conversions and mapping is generally better handled outside of InDesign, using either Acrobat Pro and or 3rd party PDF tools.
Thanks for some of the responses.
I had figured out that my document includes objects on internal pages that are showing up in CMYK SEPS output preview while K is disabled. MEaning there ARE objects that appear grey but are done in CMYK. I didn't design those items, so i'm not sure what they all are. Probably photoshop or Illustrator items. My guess is that the original designer of those objects did not specify a greyscale document.
Which leads me back to my original question about whether you can designate a page in InDesign as a grayscale only page? Probably not, I'm guessing.
Using Acrobat DC Pro's preflight tools really screws up the values of the objects when they are converted in Acrobat.
What I've taken to doing so far is simply re-outputting the PDF as a grayscale PDF from InDesign, the outputting another PDF in COlor, then using 'organize pages' in each to move the color cover pages (front/back) into the greyscale PDF from the color PDF. THis works, but seems like extra work.
Of course, the better way would be to ensure all internal pages have no CMYK objects on them. That's something I already communicated to the document creators moving forward.
It really took me a while to figure out that on the internal pages there were a couple CMYK objects. I'm glad of the SEPS preview. That really quickly identified the problem.
But again, I was hoping ther might be a way to tell my Indesign doc that the cover is CMYK, but the internal pages are greyscale.
Grayscale does not exist in InDesign as a native colour mode, however grayscale values from placed content can be passed through and maintained as grayscale mode with the correct settings.
InDesign colour conversions are very basic and offer little control. For example, if you have solid black text in the colour original, an InDesign colour conversion to grayscale will likely result in a PDF or output where the 100% black value is less than solid.
Acrobat Pro colour conversion and preflight options and/or 3rd party tools such as PitStop Pro offer a lot more control and automation – however one has to know how to use the tools correctly.
I would be happy to take a look at an “plain vanilla” PDF export direct from InDesign with no edits and offer advise on making this work in a PDF (feel free to send me a PM if you like).
Some further reading: