To answer your question directly: No easy way to do 'intelligent' color changing of marks with Core.
However, in the context of digital printing, there really are only 2 click charges: K only, or Color click charges (which are always cmyk in my experience - not cmy. So if your concern is getting charged for marks making the document print in color, there are ways to fix and control this.
First there is a way to control the color used by FreeFlow Core for the marks. Attached is a screen shot of an application on the Core server called FreeFlow Core Configure. In it there are 2 options that allow some control of how the system generates the marks. But in most cases the desire is to have all the marks in K only.
If someone places marks on the page from an application like InDesign or Quark, then typically these marks are defined as 'registration color' this means 100% of all colors used in a document. So this would cause a color click. Attached in a zip file are a couple of preflight profiles that will convert registration color to K only. Also included is a preflight that will take a specific RGB value and convert it to cmyk. That could be used to set it to 0/0/0/100 to be k only.
Typically page numbers are RGB in applications like MS Word where it is set to 'automatic' for the color. Typically this is 0,0,0 RGB. As mentioned in other replies here, color management in the RIP can be key in rendering these as K only also.
Hope this helps!
If one has content defined as R=G=B=100%, a DFE will render a color on the page. Even if the printer supports only CMY. On the FFPS DFE, there is a feature ("RGB Text and Graphics to K") that designated that R=G=B is rendered as K only. This would avoid the CMYK click charge.
You can add a custom spot color with the name "All" by editing the "custom" at the bottom of the color dropdown.
If you define it as shown in the image below, then it will print on every separation.
Does anyone know if there is an intelligent way to set the sheet mark color for an imposition so it will only use the colors contained within a particular file?
The current page number mark is set to Black, but if you inspect the mark color in PitStop, it is in fact RGB black.
This will print in CMYK during output. I'm sure I can change this color to black only, but what if I have a page that is CMY only, it won't have the page number printing in that case. What if there is a sheet with PMS colors only? I haven't tested it, but I assume it wouldn't print anything.
What I'm looking for is a mark color that will print in the colors contained within the content of a page, but not in the colors not contained in the page.
As you know, digital press clicks are frequently less expensive as black only, and if they end up being charged for 4 color clicks because of the sheet mark, it would be a very expensive mistake.