Here's a trick we use; open the grayscale in photoshop, and convert to bitmap, and when you do choose the halftone option, set it at 40 or 50 lpi, or whatever you prefer, then raise the output resolution to 1200 ppi (much cleaner dots) and save it as a .tif in bitmap mode. Then, place it in Illustrator, and since it's a bitmap, you can make it any color you have in your pallet, though in this case, white. Put the colored background behind it, and your golden. Save as a pdf or jpeg to send out the proof, and your customer gets a nice clean picture of what it will really look like, dots and all.
Steve