There are many, many different kinds of color blindness. I used to think it was only boys, but more and more women have a version of tonal blindness.
A previous poster is correct, if he told you about it, he's not ashamed of it and is willing to talk about it. Don't talk to him about fabric, quiz him on what color he sees when you see a red apple or a yellow banana. Start with basic things. This way, you can have a basic idea of what he can see as far as correctly on the spectrum and what he can see that's different from what someone else would see.
I have major problems distinguishing between pink and orange. Give me a peach, coral, shell, melon any of those and I have no clue what they are. I made a sampler once and picked what I thought was 2 pinks. One was hot pink and one was neon screaming at you for your attention orange. They totally clashed. A dear friend helped me label them as I cut out pieces. I used both of them in the same small sampler quilt. I made sure I didn't use them next to each other. The quilt turned out beautiful. When my beloved grandmother asks me if I have any of that pretty orange left, I always forget and tell her I only put pink in her quilt. It's pretty funny.