My dad has reynauds and as far as he can tell unless he's ridiculously careful and wears a million layers of very warm gloves on his hands, his hands still go white and numb when out and about. its a pretty scary thing! I hope i don't end up with it some day as i have amazing circulation
I'm still cycling in shorts and short sleeves, no gloves.
the biology about keeping your core warm is somewhat true... when your brain senses that your core temperature is lowered it contracts your bloodvessels supplying your extremeties in order to keep warm blood supplying your core body (liver most importantly) however if your extremeties are open to the environment then they will get cold before your body can react coz of windchill... your body steals your blood when your shivering and feel absolutely frozen and your lips, fingers and feet go blue/white... i doubt that happens very often on a bike if you keep moving... so its windproofing/insulating yourself for most people.