The paper says it both predicts sex, but also says gender. I am guessing what it is actually able to predict is which sex hormone is dominant. For example: If

The paper says it both predicts sex, but also says gender. I am guessing what it is actually able to predict is which sex hormone is dominant. For example: If a man with prostate cancer is taking estrogen to suppress T (and hopefully prevent the prostate cancer from growing/spreading) for even six months the colors he will perceive will shift as estrogen is dominant and the cells in his eyes will respond to that change. The paper briefly mentions this: "Others have demonstrated variation of ocular blood flow and have suggested the effect of sex hormones, but thus far, consensus is lacking".