do you know what his color deficits are? My hubby is about 40% colorblind ~ we've been trying to refine his scope, and find those borderlines of where the change is... My husband cannot see any reds lighter than 40% ~ in other words, he sees them as shades of gray, not red ~ any many yellows he doesn't see, either, unless they are over the 50% hue threshold ~ he sees them as white.
Blue seems to be one color CB people see, the most shades of it. Maybe a high contrast blue / white / red or blacks and greens with a 3rd color?