It isn't just printing in color. You used to be able to print everything in black/white or gray scale, but keep ONLY images in color (renderings, etc.). It saved you from having to change layers/annotation sets to be black/white/gray when in a layout file. They would simply be black and white by setting it to print in black/white or gray scale and you could set the layout file up to show images (and only images) in color. I found I can still set it up like this, and it will show up in my print preview, but once I actually print it (to pdf specifically) it would turn all of my images to gray scale.