I can appreciate your desire to minimize the potential for problems, but this method results in images that are virtually unprintable. Your images are going to behave as though they are screened at 1200 lines per inch. The dot gain for such a fine screen would be somewhere between 50% and 90%.

The most foolproof approach would be to colorize the images completely in Photoshop. Even this is probably overkill. If your page files are built in InDesign, it is quite possible that PDFs could be produced that most any printer can work with.