And you missed the point if you think I'm talking about color blindness (though it can factor in).
Color separation is an art of your mind, for all humans. I have been trained on this in a scientific context in university (though as a designer... I am not a researcher myself).
After the image has been processed by your eye (so this is not color blindness we're talking about here), your brain has to make artistic (not objective) decisions about how to draw lines between colors. And these lines might be rather arbitrary... Derived from cultural context among other things.
People draw different lines between color categories and it has nothing to do with how "accurate" certain peoples' eyes are.