Is he colorblind in all colors or just in some colors?
Some folks are red/green or yellow/blue colorblind yet they can see other colors just fine.
I would think you could take a picture of any colors you want to use and when you go to print the picture on your computer, use greyscale or black & white to see what the colors would do in a non-color setting. This is one of the tricks someone on this site uses for bargello quilts.