So I don't know if you know this, but I am red-green colourblind. Which is not really that fun, come to think of it. I can determine between red and green, but when they get really close in hue, I can differentiate between the two. Take, for example, this test:
I don't know if you can see it, but the only numbers I see clearly are the 56, the 25, and very very vaguely, the 29. Everything else is just random dots.
I'm apparently not alone, though, because 12-20% of white males are red-green colourblind, along with my little brother and my grandfather. I daresay it's hereditary.
Your legally (colour) blind friend,