Colour blind doesn't mean someone sees in black and white. It means they have difficulty differentiating between two colours. Often red / green, but not always.
That just proves one struggles with a lot of not well thought out assignments, not with all of them. That still means a badly designed book.
I grew up, as most of my friends, using a lot of xeroed exercise books and exercises notebooks. Monochrome copies, of course.
Never saw anyone having issues with that, weather 7 or 19 years old. If a kid struggles with monochrome computer screen, it means his learning materials are designed worse than post-soviet era 25 year old textbook.
BTW. I am eagerly waiting for better availability of eink monitors.
Red green does not mean that you ONLY have problem with those 2 colors. Means you will have problems with ANY color which is composed of some of the 2. Also there are Red/Blue Green/Blue... basically any combination. So relying in only colors is just bad design.
also, they're not the same colour to me in bright sunlight - one is light murky brown and the other is dark murky brown. under fluorescent lighting they are both the same shade of murky brown.