So there’s these three sets of cells in the eye, each tuned to a different wavelength of light, and the difference in relative activations of each cell type in response to a given light is what provides color information. Which wavelength each set of cells is tuned to varies quite a bit person to person. If your wavelength “tunings” for two types of cells are too close together, then there’s less relative difference in their activation for any given wavelength of light, and thus - in the most rigorous information-theoretic sense - there is literally less color information available.

We pick an arbitrary threshold of diminished color information and call that CVD, color vision deficiency. Depending on which threshold you pick for CVD, males are anywhere from 10 to 20 to 50 _times_ more likely to have it than females. Of course, this “has / does not have CVD” binary is an artifact of us picking a threshold; the real underlying mechanism is that the distribution of wavelength tunings in the male population is much more heavily weighted towards “overlapping”.

Put another way, you have two overlapping bell curves of “how much color information can your eye cells theoretically generate” and if you drop a single point on that graph you can capture 1% of females and 10% of males to the left of it (for that 10x figure), or 0.02% of females and 1% of males to the left of the chosen point (for that 50x figure), or anywhere in between. And the fact that you can do this tells us the two bell curves very likely have different means and standard deviations.

The search term is “spectral sensitivity” if you’re interested in finding out more.

(I do know that “but it’s true” isn’t considered to be a good rebuttal to “it’s a stereotype”, but it kinda seems like it should be, and I don’t really know why it isn’t. Also, as someone with extreme CVD, color vision is just a fantastically interesting topic regardless of sex differences. The way those EnChroma glasses that “treat” color vision deficiency work is they block out a small section of the light wavelengths where CVD tends to have high overlap. This artificially increases the relative difference in activation, meaning the brain can extract more color data, with the practical result that people with CVD put on these glasses and see colors with an intensity they’ve never seen before. But it gets even cooler! For instance, did you know if we develop the technology to directly stimulate those different wavelength receptors independently of each other, we can make those receptors report “differences in relative activation” that are literally impossible to achieve with any combination of light wavelengths? That is, the cells will happily report perfectly well-formed color data to the brain, except that it’s data in a range that no brain has ever received before. The visual cortex seems like it does fairly general information processing, at least at the lower levels before we start tagging that information with e.g. emotional responses or linguistic names, so on some level our brain would probably be able to make immediate sense of this previously “out of band” information. It must be able to do so, or else CVD sufferers wouldn’t get such vivid reactions to EnChroma glasses. So it’s very plausible that this procedure would instantly unlock actual “new color experiences” for everyone. How cool is that?)