You might be able to vary the hues a bit by color set, too, to make it so that different color block sets work well for different types of color blindness. What do you think of that? Shifting the yellow/green balance on one of them might make it so that he can use it better (and you, perhaps?), and then as other players come along with colorblindness issues, we could tweak hues on various sets to make them work for them. What do you think?