Has anyone worked with colorblind photographers / clients before?
I sure have. Speaking the language of color with people means you'll eventually run into people with various and variable color deficiencies. I've been the unfortunate one to tell several people that they are colorblind after doing a quick test or two. I think you're doing all the right things. Showing his assistant's the colorblind soft proof capability and getting him color managed. Being color managed is no less important for him than anyone else. If he's got the eye for it he'll appreciate it. Train him on what he should look for. Make him a master of color. He'll come to know what to ask of his assistants that aren't color blind. Scott Martin Onsight Precise photographic color and workflow training http://www.on-sight.com