Human eyes are entirely unique; just like fingerprints, no two sets are alike. But some genetic anomalies create especially unlikely “windows” to the world — like gray eyes. Eye experts once believed that human eyes could appear in only three colors: brown, blue, and green, sometimes with hazel or amber added.
More recently, the ashy hue that was once lumped into the blue category has been regrouped as its own, albeit rarely seen, color. Brown-eyed folks are in good company, with up to 80% of the global population sporting the shade, while blue eyes are the second most common hue.