As a website designer in my free time, I have to think about this stuff a bit, even though I have normal color vision. It's got all kinds of odd implications. For one thing, to let people with color blindness distinguish between links and ordinary text, you can't count on the colors alone -- they also need to differ in terms of how dark or light they are (and it also helps to use underlining or even clever use of borders and background color changes). They can distinguish position, of course, so they can read traffic lights the same as the rest of us -- but gods help them if some fool were to switch around the red and green lights!