If I understand correctly, based on what you said and comparing it to the rainbows on wikipedia, a trichromat would be fine with red vs green, since they are distinguishable, but nearby colors to those (red -> orange, green -> blue) look more similar (different shades of the same color). And looking into it some more, a dichromat would be fine as well because the two colors would be distinguishable because green would be essentially dark and red would be light (i.e. "the dark side goes up" in the USB example).
I've explained this in more detail before:
http://www.reddit.com/r/askscience/comments/1oomt1/how_are_r...