I wonder if there might be a language aspect to this, with males in the US generally having less familiarity with words for the in between colors leading to more difficulty distinguishing between them, with people with more words for greenish shades for example having an easier time seeing different shades of green.
I'd have to dig up references, but I understand it's a pretty well documented effect that having words for colors is directly related to a population seeing more distinction for those colors.
If I recall, some early societies didn't have a distinction between green and blue. Given that blue often doesnt show up naturally outside of the sky and it's reflections. And in those populations they would be much less sensitive to distinctions in blue-green.
For early societies, you might be thinking of the Greeks, though apparently it's somewhat common between languages?[1] For Greek the idea to originate from Homer's writings, with colors being more described in terms of how light or dark they are versus specific hues.[2]
https://boingboing.net/2011/08/12/how-language-affects-color...