> reminds me of...
As long as we are already on a tangent about rods, cones, and visual perception: one of my favorite fact is that the occasional genetic mutation that creates color blindness in men sometimes leaves a woman with "tetrachromacy". Four sets of rods and cones which increases color perception from some one-million colors to one-hundred million colors.
There was a neat story on the San Diego local news some years ago about a woman artist who was a tetrachromat. Fascinating interview. This woman said that the downside of perceiving additional colors is that something like the cereal aisle in a common supermarket could be a total sensory overload. But she of course said also that she appreciated the extra things she could see. :)