A real-world example of the need for color consistency was demonstrated by of our larger publishing clients for whom we produce full color English Language Teaching books for the Latin American market. Because they used to out-source the design work to numerous designers and had no rigid color management policy, the thousands of photos and illustrations which appeared in their books had goodness knows how many different color profiles assigned to them. The results were often horrific - the images varied from too dark to too light to strangely hued, all in the same book.
To combat this problem, rigid color management policies were introduced, and every image and document now has the color setting Europe ISO Coated FOGRA27 applied, and all Grayscale images have Gamma 2.2 applied. This has resolved the problem and color is now consistent throughout all published titles.
I could write an explanation of what all the color management jargon means, and suggest exactly what settings would be best for you to use, but luckily for me, it's already been done by Ian Lyons of computer-darkroom.com (click here for a comprehensive color management article) Ian has been writing about color management in Photoshop since 1998, and his latest article covers CS4.
For my own part, all I can suggest is that you should BE CONSISTENT. Although there will always be an element of risk when you try different things, as long as your color settings are consistent, you are reducing the margin for error. Secondly, check and double check your layout and image documents before sending them to press...
If you check your documents thoroughly before sending them to press, there should be no problems with the output. This means that you need to make sure all the images have the same color profile assigned, there are no rogue spot colors in the document, no RGB images mixed in with CMYK, no low resolution images (300DPI for raster images, 1200DPI for Photoshop Bitmap line art) and so on. Obviously all the fonts need to be present and correct as well.
InDesign CS4 Live Preflight
Adobe InDesign has a live Preflight panel which seems to be somewhat limited, and it slows down the workflow. However, it's certainly better than nothing. You can create your own rules, although I haven't found any means of identifying mis-matched color profiles as yet. Below is a screen shot of the panel identifying an RGB image. I deliberately assigned a different color profile to another image, but this wasn't highlighted.
If you're willing to wait around for InDesign to Preflight a large document, then you might as well spend a bit more and get the job done properly with something like Markzware Flightcheck Professional.
Markzware Flightcheck Professional
I've been using one or other version of Markzware FlightCheck for years and I think it's the best there is for preflighting either an InDesign or Quark XPress document pre-press (it doesn’t require the native applications to run). Below is a screenshot of the results that were returned for the same document as shown above. These results can be as simple or complex as you like - it's all highly customizable.
For an overview of Flightcheck, below is a Markzware video showing a brief walkthrough. One potential downside is that at the time of writing, Flightcheck doesn't support InDesign CS4 or Quark XPress 8 - just CS3 and Q7. To get around this I exported a file from InDesign CS4 as an InDesign CS3 Interchange File, opened it in CS3, saved it as an .indd file and Flightcheck processed it fine. The same could be done with a Quark file. No doubt Markzware will catch up soon.
Markzware Flightcheck Professional Video