If a GN4 page contains only color images and not other elements in color, you can select Convert to GRAY option in the Images Color Conversion on the Output tab of the print preset - and then print with that preset:

Result is that color images are printed as grayscale, but colored text and boxes are still in color (the same limitation as in GN3).

 

There are workarounds that can be temporarily implemented, like having a post process that converts the color PDF to grayscale.

Here you can find some hint about how to implement it:

•Manual method: http://forums.adobe.com/message/4252946. In the reply #2 it's explained how to use the "Color Conversion" Print production tool;

•Semi-automatic method: http://blogs.adobe.com/acrolaw/2009/10/converting-color-pdf-to-greyscale-pdf-an-update/ explains how to create an Acrobat droplet;

•Automatic method: using GhostScript:

gswin64.exe -sOutputFile=your_output_file.pdf -sDEVICE=pdfwrite -sColorConversionStrategy=Gray -dBATCH -dNOPAUSE -dProcessColorModel=/DeviceGray -dCompatibilityLevel=1.4 your_input_file.pdf

It requires GhostScript (http://www.ghostscript.com/) to be installed on the server and some extra external scripting.